title: M1919 Browning machine gun

text: The conversions were performed from 1966 through 1967 at Naval Ordnance Station Louisville. Modified M1919A4s had the designation ""Machine Gun, 7.62mm / Mk 21 Mod 0"" stamped on the receiver sideplate in 1/4-inch lettering. The replacement barrels had ""7.62mm NATO-G"" stamped on them in 1/8-inch letters to differentiate them from M1919A4 or M60 barrels; the letter "G" indicated it used a grooved barrel bushing.


title: M1919 Browning machine gun

text: It used the standard 7.62mm NATO M13 link "strip-out" disintegrating link, in which the bolt pushes the round out of the bottom of the two-part link and then forwards into the breech. The old M1 link "pull-out" disintegrating links, which are pulled backwards out of the one-piece link by the extractor towards the bolt and then forwards into the breech, would not feed through the new mechanism. The M1 links, which were designed for the longer and thinner .30-06 Springfield, would also be too narrow to fit the shorter and thicker 7.62mm NATO round. The US Navy, because of their narrower inventory of 7.62mm NATO ammunition, used linked belts of either 7.62mm M80 Ball or a 4:1 ratio mix of 7.62mm M80 Ball and 7.62mm M62 Tracer.


title: M1919 Browning machine gun

text: The refurbished feed mechanism was left-hand feed only. It was different from the one in the M60 GPMG in that the open end of the belt had to be on top so it could be stripped out. To prepare the ammo, gunners had to take out both of the 100-round belts from an M19A1 ammo can, had to link them both together, and then loaded the resultant 200-round belt back into the M19A1 can upside-down so it would feed correctly.


title: M1919 Browning machine gun

text: The M1919 pattern has been used in countries all over the world in a variety of forms and under a number of different designations.


title: M1919 Browning machine gun

text: Colt produced a derivative of the M2 aircraft machine gun, the Colt MG40. It shipped in a variety of calibers, including the basic .30-06 Springfield and popular 7mm Spanish Mauser, and was available in left- or right-hand feed. The MG40-2 Light Aircraft Machine Gun could be used in flexible- (pintle-mounted), fixed- (wing-mounted), or synchronized- (through the propeller) models. The Flexible mount machine gun came with grips and a "butterfly" trigger plate like the standard ground model. The Fixed model had a backplate. It used a cable connected to an operating slide connected to a stud on the bolt to fire it; tension in the cable causes the trigger to activate and slack in the cable causes it to stop. The synchronized variant of the Fixed model had a trigger motor for through-propeller, gun synchronizing needs.


title: M1919 Browning machine gun

text: FN Herstal developed a family of machine guns analogical to Colt's commercial line in 1930s, and those, even though not well-known, were used by many European countries during WWII


title: M1919 Browning machine gun

text: The Browning M1919 remains popular with civilian enthusiasts in the United States, though changes in 1986 to the National Firearms Act of 1934 (the US Federal law regulating private ownership of machine guns) prohibited the registration of new machine guns for sales to civilians, thus freezing the number of "transferable" machine guns in private ownership. The inflation of prices that followed, and the availability of parts from surplussed and scrapped machine guns, led to the development of semi-automatic versions of the Browning M1919. Typically, these are built using a new right sideplate (the portion legally considered the "firearm" under US law), which has a raised "island" protruding into the interior of the receiver. This requires the use of a modified bolt, barrel extension and lock frame which have been designed to allow only semi-automatic firing. The "island" prevents the insertion of unmodified full-automatic parts. A number of small gun companies have produced these "semi-auto machine guns" for commercial sales. The fairly simple modifications necessary to convert M1919 parts to the semi-automatic version, and the relatively easy process of riveting used in the assembly of the Browning machine gun's receiver, have also made it a popular gun for hobbyists to build at home.


title: M1919 Browning machine gun

text: Similar "semi-auto machine guns" have been built using parts from other Browning pattern machine guns, to include the AN/M2 aircraft gun and FN30, and variations that never saw military use such as extremely short (8") barreled guns.


title: Asteroid belt

text: The asteroid belt is a torus-shaped region in the Solar System, located roughly between the orbits of the planets Jupiter and Mars. It contains a great many solid, irregularly shaped bodies, of many sizes, but much smaller than planets, called asteroids or minor planets. This asteroid belt is also called the main asteroid belt or main belt to distinguish it from other asteroid populations in the Solar System such as near-Earth asteroids and trojan asteroids.


title: Asteroid belt

text: The asteroid belt is the smallest and innermost known circumstellar disc in the Solar System. About 60% of its mass is contained in the four largest asteroids: Ceres, Vesta, Pallas, and Hygiea. The total mass of the asteroid belt is calculated to be 3% that of the Moon.


title: Asteroid belt

text: Ceres, the only object in the asteroid belt large enough to be a dwarf planet, is about 950 km in diameter, whereas Vesta, Pallas, and Hygiea have mean diameters less than 600 km. The remaining bodies range down to the size of a dust particle. The asteroid material is so thinly distributed that numerous unmanned spacecraft have traversed it without incident. Nonetheless, collisions between large asteroids occur and can produce an asteroid family, whose members have similar orbital characteristics and compositions. Individual asteroids within the belt are categorized by their spectra, with most falling into three basic groups: carbonaceous (C-type), silicate (S-type), and metal-rich (M-type).


title: Asteroid belt

text: The asteroid belt formed from the primordial solar nebula as a group of planetesimals. Planetesimals are the smaller precursors of the protoplanets. Between Mars and Jupiter, however, gravitational perturbations from Jupiter imbued the protoplanets with too much orbital energy for them to accrete into a planet. Collisions became too violent, and instead of fusing together, the planetesimals and most of the protoplanets shattered. As a result, 99.9% of the asteroid belt's original mass was lost in the first 100 million years of the Solar System's history. Some fragments eventually found their way into the inner Solar System, leading to meteorite impacts with the inner planets. Asteroid orbits continue to be appreciably perturbed whenever their period of revolution about the Sun forms an orbital resonance with Jupiter. At these orbital distances, a Kirkwood gap occurs as they are swept into other orbits.


title: Asteroid belt

text: Classes of small Solar System bodies in other regions are the near-Earth objects, the centaurs, the Kuiper belt objects, the scattered disc objects, the sednoids, and the Oort cloud objects.


title: Asteroid belt

text: On 22 January 2014, European Space Agency (ESA) scientists reported the detection, for the first definitive time, of water vapor on Ceres, the largest object in the asteroid belt. The detection was made by using the far-infrared abilities of the Herschel Space Observatory. The finding was unexpected because comets, not asteroids, are typically considered to "sprout jets and plumes". According to one of the scientists, "The lines are becoming more and more blurred between comets and asteroids".


title: Asteroid belt

text: In 1596, Johannes Kepler wrote, "Between Mars and Jupiter, I place a planet," in his "Mysterium Cosmographicum", stating his prediction that a planet would be found there. While analyzing Tycho Brahe's data, Kepler thought that too large a gap existed between the orbits of Mars and Jupiter to fit Kepler’s then-current model of where planetary orbits should be found.


title: Asteroid belt

text: In an anonymous footnote to his 1766 translation of Charles Bonnet's "Contemplation de la Nature", the astronomer Johann Daniel Titius of Wittenberg noted an apparent pattern in the layout of the planets, now known as the Titius-Bode Law. If one began a numerical sequence at 0, then included 3, 6, 12, 24, 48, etc., doubling each time, and added four to each number and divided by 10, this produced a remarkably close approximation to the radii of the orbits of the known planets as measured in astronomical units, "provided" one allowed for a "missing planet" (equivalent to 24 in the sequence) between the orbits of Mars (12) and Jupiter (48). In his footnote, Titius declared, "But should the Lord Architect have left that space empty? Not at all." When William Herschel discovered Uranus in 1781, the planet's orbit matched the law almost perfectly, leading astronomers to conclude that a planet had to be between the orbits of Mars and Jupiter.


title: Asteroid belt

text: On January 1, 1801, Giuseppe Piazzi, chairman of astronomy at the University of Palermo, Sicily, found a tiny moving object in an orbit with exactly the radius predicted by this pattern. He dubbed it "Ceres", after the Roman goddess of the harvest and patron of Sicily. Piazzi initially believed it to be a comet, but its lack of a coma suggested it was a planet.


title: Asteroid belt

text: Thus, the aforementioned pattern predicted the semimajor axes of all eight planets of the time (Mercury, Venus, Earth, Mars, Ceres, Jupiter, Saturn, and Uranus). Concurrent with the discovery of Ceres, an informal group of 24 astronomers dubbed the "celestial police" was formed under the invitation of Franz Xaver von Zach with the express purpose of finding additional planets; they focused their search for them in the region between Mars and Jupiter where the Titius–Bode law predicted there should be a planet.


title: Asteroid belt

text: About 15 months later, Heinrich Olbers, a member of the celestial police, discovered a second object in the same region, Pallas. Unlike the other known planets, Ceres and Pallas remained points of light even under the highest telescope magnifications instead of resolving into discs. Apart from their rapid movement, they appeared indistinguishable from stars.


title: Asteroid belt

text: Accordingly, in 1802, William Herschel suggested they be placed into a separate category, named "asteroids", after the Greek "asteroeides", meaning "star-like". Upon completing a series of observations of Ceres and Pallas, he concluded,


title: Asteroid belt

text: Neither the appellation of planets nor that of comets can with any propriety of language be given to these two stars ... They resemble small stars so much as hardly to be distinguished from them. From this, their asteroidal appearance, if I take my name, and call them Asteroids; reserving for myself, however, the liberty of changing that name, if another, more expressive of their nature, should occur.


title: Asteroid belt

text: By 1807, further investigation revealed two new objects in the region: Juno and Vesta. The burning of Lilienthal in the Napoleonic wars, where the main body of work had been done, brought this first period of discovery to a close.


title: Asteroid belt

text: Despite Herschel's coinage, for several decades it remained common practice to refer to these objects as planets and to prefix their names with numbers representing their sequence of discovery: 1 Ceres, 2 Pallas, 3 Juno, 4 Vesta. In 1845, though, astronomers detected a fifth object (5 Astraea) and, shortly thereafter, new objects were found at an accelerating rate. Counting them among the planets became increasingly cumbersome. Eventually, they were dropped from the planet list (as first suggested by Alexander von Humboldt in the early 1850s) and Herschel's coinage, "asteroids", gradually came into common use.


title: Asteroid belt

text: The discovery of Neptune in 1846 led to the discrediting of the Titius–Bode law in the eyes of scientists because its orbit was nowhere near the predicted position. To date, no scientific explanation for the law has been given, and astronomers' consensus regards it as a coincidence.


title: Asteroid belt

text: The expression "asteroid belt" came into use in the early 1850s, although pinpointing who coined the term is difficult. The first English use seems to be in the 1850 translation (by Elise Otté) of Alexander von Humboldt's "Cosmos": "[...] and the regular appearance, about the 13th of November and the 11th of August, of shooting stars, which probably form part of a belt of asteroids intersecting the Earth's orbit and moving with planetary velocity". Another early appearance occurred in Robert James Mann's "A Guide to the Knowledge of the Heavens": "The orbits of the asteroids are placed in a wide belt of space, extending between the extremes of [...]". The American astronomer Benjamin Peirce seems to have adopted that terminology and to have been one of its promoters.


title: Asteroid belt

text: Over 100 asteroids had been located by mid-1868, and in 1891, the introduction of astrophotography by Max Wolf accelerated the rate of discovery still further. A total of 1,000 asteroids had been found by 1921, 10,000 by 1981, and 100,000 by 2000. Modern asteroid survey systems now use automated means to locate new minor planets in ever-increasing numbers.


title: Asteroid belt

text: In 1802, shortly after discovering Pallas, Olbers suggested to Herschel that Ceres and Pallas were fragments of a much larger planet that once occupied the Mars–Jupiter region, with this planet having suffered an internal explosion or a cometary impact many million years before, while Odessan astronomer K. N. Savchenko suggested that Ceres, Pallas, Juno, and Vesta were escaped moons rather than fragments of the exploded planet. The large amount of energy required to destroy a planet, combined with the belt's low combined mass, which is only about 4% of the mass of Earth's Moon, does not support these hypotheses. Further, the significant chemical differences between the asteroids become difficult to explain if they come from the same planet.


title: Asteroid belt

text: A hypothesis for the asteroid belt’s creation relates to how, in general for the Solar System, planetary formation is thought to have occurred via a process comparable to the long-standing nebular hypothesis; a cloud of interstellar dust and gas collapsed under the influence of gravity to form a rotating disc of material that then further condensed to form the Sun and planets. During the first few million years of the Solar System's history, an accretion process of sticky collisions caused the clumping of small particles, which gradually increased in size. Once the clumps reached sufficient mass, they could draw in other bodies through gravitational attraction and become planetesimals. This gravitational accretion led to the formation of the planets.


title: Asteroid belt

text: Planetesimals within the region that would become the asteroid belt were too strongly perturbed by Jupiter's gravity to form a planet. Instead, they continued to orbit the Sun as before, occasionally colliding. In regions where the average velocity of the collisions was too high, the shattering of planetesimals tended to dominate over accretion, preventing the formation of planet-sized bodies. Orbital resonances occurred where the orbital period of an object in the belt formed an integer fraction of the orbital period of Jupiter, perturbing the object into a different orbit; the region lying between the orbits of Mars and Jupiter contains many such orbital resonances. As Jupiter migrated inward following its formation, these resonances would have swept across the asteroid belt, dynamically exciting the region's population and increasing their velocities relative to each other.


title: Asteroid belt

text: During the early history of the Solar System, the asteroids melted to some degree, allowing elements within them to be partially or completely differentiated by mass. Some of the progenitor bodies may even have undergone periods of explosive volcanism and formed magma oceans. Because of the relatively small size of the bodies, though, the period of melting was necessarily brief (compared to the much larger planets), and had generally ended about 4.5 billion years ago, in the first tens of millions of years of formation. In August 2007, a study of zircon crystals in an Antarctic meteorite believed to have originated from Vesta suggested that it, and by extension the rest of the asteroid belt, had formed rather quickly, within 10 million years of the Solar System's origin.


title: Asteroid belt

text: The asteroids are not samples of the primordial Solar System. They have undergone considerable evolution since their formation, including internal heating (in the first few tens of millions of years), surface melting from impacts, space weathering from radiation, and bombardment by micrometeorites. Although some scientists refer to the asteroids as residual planetesimals, other scientists consider them distinct.


title: Asteroid belt

text: The current asteroid belt is believed to contain only a small fraction of the mass of the primordial belt. Computer simulations suggest that the original asteroid belt may have contained mass equivalent to the Earth's. Primarily because of gravitational perturbations, most of the material was ejected from the belt within about 1 million years of formation, leaving behind less than 0.1% of the original mass. Since its formation, the size distribution of the asteroid belt has remained relatively stable; no significant increase or decrease in the typical dimensions of the main-belt asteroids has occurred.


title: Asteroid belt

text: The 4:1 orbital resonance with Jupiter, at a radius 2.06 astronomical units (AUs), can be considered the inner boundary of the asteroid belt. Perturbations by Jupiter send bodies straying there into unstable orbits. Most bodies formed within the radius of this gap were swept up by Mars (which has an aphelion at 1.67 AU) or ejected by its gravitational perturbations in the early history of the Solar System. The Hungaria asteroids lie closer to the Sun than the 4:1 resonance, but are protected from disruption by their high inclination.


title: Asteroid belt

text: When the asteroid belt was first formed, the temperatures at a distance of 2.7 AU from the Sun formed a "snow line" below the freezing point of water. Planetesimals formed beyond this radius were able to accumulate ice.


title: Asteroid belt

text: In 2006, a population of comets had been discovered within the asteroid belt beyond the snow line, which may have provided a source of water for Earth's oceans. According to some models, outgassing of water during the Earth's formative period was insufficient to form the oceans, requiring an external source such as a cometary bombardment.


title: Asteroid belt

text: The outer asteroid belt appears to include a few objects that may have arrived there during the last few hundred years, the list includes also known as 362P.


title: Asteroid belt

text: Contrary to popular imagery, the asteroid belt is mostly empty. The asteroids are spread over such a large volume that reaching an asteroid without aiming carefully would be improbable. Nonetheless, hundreds of thousands of asteroids are currently known, and the total number ranges in the millions or more, depending on the lower size cutoff. Over 200 asteroids are known to be larger than 100 km, and a survey in the infrared wavelengths has shown that the asteroid belt has between 700,000 and 1.7 million asteroids with a diameter of 1 km or more. The absolute magnitudes of most of the known asteroids are between 11 and 19, with the median at about 16.


title: Asteroid belt

text: The total mass of the asteroid belt is estimated to be kg, which is just 3% of the mass of the Moon. The four largest objects, Ceres, Vesta, Pallas, and Hygiea, account for maybe 62% of the belt's total mass, with 39% accounted for by Ceres alone.


title: Asteroid belt

text: The current belt consists primarily of three categories of asteroids: C-type or carbonaceous asteroids, S-type or silicate asteroids, and M-type or metallic asteroids.


title: Asteroid belt

text: Carbonaceous asteroids, as their name suggests, are carbon-rich. They dominate the asteroid belt's outer regions. Together they comprise over 75% of the visible asteroids. They are redder in hue than the other asteroids and have a very low albedo. Their surface compositions are similar to carbonaceous chondrite meteorites. Chemically, their spectra match the primordial composition of the early Solar System, with only the lighter elements and volatiles removed.


title: Asteroid belt

text: S-type (silicate-rich) asteroids are more common toward the inner region of the belt, within 2.5 AU of the Sun. The spectra of their surfaces reveal the presence of silicates and some metal, but no significant carbonaceous compounds. This indicates that their materials have been significantly modified from their primordial composition, probably through melting and reformation. They have a relatively high albedo and form about 17% of the total asteroid population.


title: Asteroid belt

text: M-type (metal-rich) asteroids form about 10% of the total population; their spectra resemble that of iron-nickel. Some are believed to have formed from the metallic cores of differentiated progenitor bodies that were disrupted through collision. However, some silicate compounds also can produce a similar appearance. For example, the large M-type asteroid 22 Kalliope does not appear to be primarily composed of metal. Within the asteroid belt, the number distribution of M-type asteroids peaks at a semimajor axis of about 2.7 AU. Whether all M-types are compositionally similar, or whether it is a label for several varieties which do not fit neatly into the main C and S classes is not yet clear.


title: Asteroid belt

text: One mystery of the asteroid belt is the relative rarity of V-type (Vestoid) or basaltic asteroids. Theories of asteroid formation predict that objects the size of Vesta or larger should form crusts and mantles, which would be composed mainly of basaltic rock, resulting in more than half of all asteroids being composed either of basalt or olivine. Observations, however, suggest that 99% of the predicted basaltic material is missing. Until 2001, most basaltic bodies discovered in the asteroid belt were believed to originate from the asteroid Vesta (hence their name V-type), but the discovery of the asteroid 1459 Magnya revealed a slightly different chemical composition from the other basaltic asteroids discovered until then, suggesting a different origin. This hypothesis was reinforced by the further discovery in 2007 of two asteroids in the outer belt, 7472 Kumakiri and , with a differing basaltic composition that could not have originated from Vesta. These latter two are the only V-type asteroids discovered in the outer belt to date.


title: Asteroid belt

text: The temperature of the asteroid belt varies with the distance from the Sun. For dust particles within the belt, typical temperatures range from 200 K (−73 °C) at 2.2 AU down to 165 K (−108 °C) at 3.2 AU. However, due to rotation, the surface temperature of an asteroid can vary considerably as the sides are alternately exposed to solar radiation and then to the stellar background.


title: Asteroid belt

text: Several otherwise unremarkable bodies in the outer belt show cometary activity. Because their orbits cannot be explained through the capture of classical comets, many of the outer asteroids are thought to be icy, with the ice occasionally exposed to sublimation through small impacts. Main-belt comets may have been a major source of the Earth's oceans because the deuterium-hydrogen ratio is too low for classical comets to have been the principal source.


title: Asteroid belt

text: Most asteroids within the asteroid belt have orbital eccentricities less than 0.4, and an inclination of less than 30°. The orbital distribution of the asteroids reaches a maximum at an eccentricity around 0.07 and an inclination below 4°. Thus, although a typical asteroid has a relatively circular orbit and lies near the plane of the ecliptic, some asteroid orbits can be highly eccentric or travel well outside the ecliptic plane.


title: Asteroid belt

text: Sometimes, the term "main belt" is used to refer only to the more compact "core" region where the greatest concentration of bodies is found. This lies between the strong 4:1 and 2:1 Kirkwood gaps at 2.06 and 3.27 AU, and at orbital eccentricities less than roughly 0.33, along with orbital inclinations below about 20°. , this "core" region contained 93% of all discovered and numbered minor planets within the Solar System. The JPL Small-Body Database lists over 1 million known main-belt asteroids.


title: Asteroid belt

text: The semimajor axis of an asteroid is used to describe the dimensions of its orbit around the Sun, and its value determines the minor planet's orbital period. In 1866, Daniel Kirkwood announced the discovery of gaps in the distances of these bodies' orbits from the Sun. They were located in positions where their period of revolution about the Sun was an integer fraction of Jupiter's orbital period. Kirkwood proposed that the gravitational perturbations of the planet led to the removal of asteroids from these orbits.


title: Asteroid belt

text: When the mean orbital period of an asteroid is an integer fraction of the orbital period of Jupiter, a mean-motion resonance with the gas giant is created that is sufficient to perturb an asteroid to new orbital elements. Asteroids that become located in the gap orbits (either primordially because of the migration of Jupiter's orbit, or due to prior perturbations or collisions) are gradually nudged into different, random orbits with a larger or smaller semimajor axis.


title: Asteroid belt

text: The high population of the asteroid belt makes for a very active environment, where collisions between asteroids occur frequently (on astronomical time scales). Collisions between main-belt bodies with a mean radius of 10 km are expected to occur about once every 10 million years. A collision may fragment an asteroid into numerous smaller pieces (leading to the formation of a new asteroid family). Conversely, collisions that occur at low relative speeds may also join two asteroids. After more than 4 billion years of such processes, the members of the asteroid belt now bear little resemblance to the original population.


title: Asteroid belt

text: Along with the asteroid bodies, the asteroid belt also contains bands of dust with particle radii of up to a few hundred micrometres. This fine material is produced, at least in part, from collisions between asteroids, and by the impact of micrometeorites upon the asteroids. Due to the Poynting–Robertson effect, the pressure of solar radiation causes this dust to slowly spiral inward toward the Sun.


title: Asteroid belt

text: The combination of this fine asteroid dust, as well as ejected cometary material, produces the zodiacal light. This faint auroral glow can be viewed at night extending from the direction of the Sun along the plane of the ecliptic. Asteroid particles that produce the visible zodiacal light average about 40 μm in radius. The typical lifetimes of main-belt zodiacal cloud particles are about 700,000 years. Thus, to maintain the bands of dust, new particles must be steadily produced within the asteroid belt. It was once thought that collisions of asteroids form a major component of the zodiacal light. However, computer simulations by Nesvorný and colleagues attributed 85 percent of the zodiacal-light dust to fragmentations of Jupiter-family comets, rather than to comets and collisions between asteroids in the asteroid belt. At most 10 percent of the dust is attributed to the asteroid belt.


title: Asteroid belt

text: Some of the debris from collisions can form meteoroids that enter the Earth's atmosphere. Of the 50,000 meteorites found on Earth to date, 99.8 percent are believed to have originated in the asteroid belt.


title: Asteroid belt

text: In 1918, the Japanese astronomer Kiyotsugu Hirayama noticed that the orbits of some of the asteroids had similar parameters, forming families or groups.


title: Asteroid belt

text: Approximately one-third of the asteroids in the asteroid belt are members of an asteroid family. These share similar orbital elements, such as semi-major axis, eccentricity, and orbital inclination as well as similar spectral features, all of which indicate a common origin in the breakup of a larger body. Graphical displays of these elements, for members of the asteroid belt, show concentrations indicating the presence of an asteroid family. There are about 20 to 30 associations that are almost certainly asteroid families. Additional groupings have been found that are less certain. Asteroid families can be confirmed when the members display spectral features. Smaller associations of asteroids are called groups or clusters.


title: Asteroid belt

text: Some of the most prominent families in the asteroid belt (in order of increasing semi-major axes) are the Flora, Eunomia, Koronis, Eos, and Themis families. The Flora family, one of the largest with more than 800 known members, may have formed from a collision less than 1 billion years ago.


title: Asteroid belt

text: The largest asteroid to be a true member of a family (as opposed to an interloper in the case of Ceres with the Gefion family) is 4 Vesta. The Vesta family is believed to have formed as the result of a crater-forming impact on Vesta. Likewise, the HED meteorites may also have originated from Vesta as a result of this collision.


title: Asteroid belt

text: Three prominent bands of dust have been found within the asteroid belt. These have similar orbital inclinations as the Eos, Koronis, and Themis asteroid families, and so are possibly associated with those groupings.


title: Asteroid belt

text: The main belt evolution after the Late Heavy Bombardment was very likely affected by the passages of large Centaurs and trans-Neptunian objects (TNOs).


title: Asteroid belt

text: Centaurs and TNOs that reach the inner Solar System can modify the orbits of main belt asteroids, though only if their mass is of the order of for single encounters or, one order less in case of multiple close encounters.


title: Asteroid belt

text: However Centaurs and TNOs are unlikely to have significantly dispersed young asteroid families in the main belt, but they can have perturbed some old asteroid families. Current main belt asteroids that originated as Centaurs or trans-Neptunian objects may lie in the outer belt with short lifetime of less than 4 million years, most likely between 2.8 and 3.2 AU at larger eccentricities than typical of main belt asteroid.


title: Asteroid belt

text: Skirting the inner edge of the belt (ranging between 1.78 and 2.0 AU, with a mean semi-major axis of 1.9 AU) is the Hungaria family of minor planets. They are named after the main member, 434 Hungaria; the group contains at least 52 named asteroids. The Hungaria group is separated from the main body by the 4:1 Kirkwood gap and their orbits have a high inclination. Some members belong to the Mars-crossing category of asteroids, and gravitational perturbations by Mars are likely a factor in reducing the total population of this group.


title: Asteroid belt

text: Another high-inclination group in the inner part of the asteroid belt is the Phocaea family. These are composed primarily of S-type asteroids, whereas the neighboring Hungaria family includes some E-types. The Phocaea family orbit between 2.25 and 2.5 AU from the Sun.


title: Asteroid belt

text: Skirting the outer edge of the asteroid belt is the Cybele group, orbiting between 3.3 and 3.5 AU. These have a 7:4 orbital resonance with Jupiter. The Hilda family orbit between 3.5 and 4.2 AU, and have relatively circular orbits and a stable 3:2 orbital resonance with Jupiter. There are few asteroids beyond 4.2 AU, until Jupiter's orbit. Here the two families of Trojan asteroids can be found, which, at least for objects larger than 1 km, are approximately as numerous as the asteroids of the asteroid belt.


title: Asteroid belt

text: Some asteroid families have formed recently, in astronomical terms. The Karin family apparently formed about 5.7 million years ago from a collision with a progenitor asteroid 33 km in radius. The Veritas family formed about 8.3 million years ago; evidence includes interplanetary dust recovered from ocean sediment.


title: Asteroid belt

text: More recently, the Datura cluster appears to have formed about 530,000 years ago from a collision with a main-belt asteroid. The age estimate is based on the probability of the members having their current orbits, rather than from any physical evidence. However, this cluster may have been a source for some zodiacal dust material. Other recent cluster formations, such as the Iannini cluster ( million years ago), may have provided additional sources of this asteroid dust.


title: Asteroid belt

text: The first spacecraft to traverse the asteroid belt was "Pioneer 10", which entered the region on 16 July 1972. At the time there was some concern that the debris in the belt would pose a hazard to the spacecraft, but it has since been safely traversed by 12 spacecraft without incident. "Pioneer 11", "Voyagers 1" and "2" and "Ulysses" passed through the belt without imaging any asteroids. "Galileo" imaged 951 Gaspra in 1991 and 243 Ida in 1993, NEAR imaged 253 Mathilde in 1997 and landed on 433 Eros in February 2001, "Cassini" imaged 2685 Masursky in 2000, "Stardust" imaged 5535 Annefrank in 2002, "New Horizons" imaged 132524 APL in 2006, "Rosetta" imaged 2867 Šteins in September 2008 and 21 Lutetia in July 2010, and "Dawn" orbited Vesta between July 2011 and September 2012 and has orbited Ceres since March 2015. On its way to Jupiter, "Juno" traversed the asteroid belt without collecting science data. Due to the low density of materials within the belt, the odds of a probe running into an asteroid are now estimated at less than 1 in 1 billion.


title: Asteroid belt

text: Most belt asteroids imaged to date have come from brief flyby opportunities by probes headed for other targets. Only the "Dawn", NEAR Shoemaker and "Hayabusa" missions have studied asteroids for a protracted period in orbit and at the surface.


title: Chris Weidman

text: Christopher James Weidman (born June 17, 1984) is an American professional mixed martial artist. He is signed to the Ultimate Fighting Championship (UFC), where he competes in the middleweight division. He is a former UFC Middleweight Champion.


title: Chris Weidman

text: An accomplished amateur wrestler, Weidman was a two-time NJCAA All-American and a two-time NCAA Division I All-American during his collegiate career. He began his mixed martial arts career in 2008, and joined the UFC in 2011, soon amassing a 9–0 record. In 2013, Weidman came to worldwide prominence by defeating Anderson Silva to win the UFC Middleweight Championship. This ended Silva's 16-fight winning streak inside the UFC and his seven-year reign as the champion. Weidman retained the title for two and a half years, defending it three times before losing it to Luke Rockhold.


title: Chris Weidman

text: Weidman was born in Baldwin, New York, on June 17, 1984, the second of three children. He is of German and Irish descent and was raised as a Lutheran. He and his older brother were involved in numerous athletic activities. Chris started wrestling at a very young age. With his natural athleticism, he mastered the sport very quickly. He attended Baldwin Senior High School on Long Island where he was a Nassau County and New York state wrestling champion.


title: Chris Weidman

text: A standout in college, he earned All-American wrestling honors twice at Nassau Community College before transferring to Hofstra. He became the first junior college wrestler in history to be an NYS Collegiate Champion. At Hofstra, he became a two-time NCAA Division I All-American, placing sixth at the 06' NCAA championships his junior year and third at the 07' NCAA's his senior year. Weidman graduated from Hofstra University with a bachelor's degree in psychology. He was later a wrestling instructor of the university.


title: Chris Weidman

text: Weidman met Gabriel "Monsta" Toribio while attending Hofstra who invited Weidman to come to Matt and Nick Serra's BJJ Academy a few miles from campus in Levittown, New York to help some of the fighters with their wrestling. Weidman also took some submission grappling classes and within three months he competed in and won The East Coast Grappler's Quest in his weight class and the Absolute Division with all 13 matches ending in submissions.


title: Chris Weidman

text: With full-time assistant coaching and graduate school at Hofstra, grappling had to be put on hold for a while. While coaching, Weidman trained for the Olympic trials. When his dream was not attained, Weidman had to decide if he wanted to continue training for the world teams and Olympics or give MMA a shot. Toribio brought Weidman to Ray Longo's MMA Academy and introduced Weidman to Longo. With his noticeable technique and skills, Weidman was encouraged to train full-time to fight. In 2011, Longo and Weidman LAW MMA opened, where they are instructors, owners, and operators in Garden City, New York.


title: Chris Weidman

text: After winning the ADCC East Coast Trials, Weidman qualified for and competed at the 2009 ADCC Submission Wrestling World Championship (with one year of formal submission grappling training) in Barcelona where he lost in a quarter-final match-up.


title: Chris Weidman

text: Weidman made his MMA professional debut representing the Serra-Longo Fight Team in February 2009 in Louis Neglia's Ring of Combat 23. He fought as a Middleweight against Reuben Lopes, whom he submitted quickly via kimura, at 1:35 of the first round. Two months later at Ring of Combat 24, he stopped Mike Stewart with punches in the first round.


title: Chris Weidman

text: In his third bout, Weidman won the Ring of Combat middleweight title on September 24, 2010, by defeating Uriah Hall at Ring of Combat 31 via punches in the first round. Weidman defended the ROC Middleweight Championship on December 3, 2010, at Ring of Combat 33 with an impressive victory over Valdir Araujo via unanimous decision. By this point Weidman was being called "one of the most highly-touted blue chip middleweight prospects ever". Weidman was offered contracts by numerous organizations, but Weidman elected to wait until the UFC offered him a contract, which he quickly accepted.


title: Chris Weidman

text: Weidman made his UFC debut against Alessio Sakara on March 3, 2011, at , replacing an injured Rafael Natal. Weidman, who took the fight on two weeks' notice and who was also nursing a rib injury, won a unanimous decision, scoring a decisive 30–27 on all three judges' scorecards.


title: Chris Weidman

text: Weidman faced Jesse Bongfeldt on June 11, 2011, at UFC 131, replacing an injured Court McGee. Weidman defeated Bongfeldt via first round standing guillotine choke, earning "Submission of the Night" honors.


title: Chris Weidman

text: Weidman next faced Tom Lawlor on November 19, 2011, at UFC 139. He won the fight via technical submission, rendering Lawlor unconscious with a D'Arce choke in the first round.


title: Chris Weidman

text: Weidman defeated Demian Maia by unanimous decision (29–28, 30–27, and 29–28) on January 28, 2012, at UFC on Fox 2. The fight was initially announced as a split decision but the judges actually scored it as a unanimous decision, clarified by UFC President Dana White in a tweet. Weidman replaced Michael Bisping on eleven days' notice after Mark Muñoz was forced out of his fight with Chael Sonnen. Bisping was chosen to take Munoz's place in the co-main event.


title: Chris Weidman

text: Weidman faced Mark Muñoz on July 11, 2012, at . Weidman dominated Munoz throughout first round using his wrestling skills. In the second round, he knocked out Munoz with a counter elbow to the forehead followed by ground and pound to an unconscious Munoz, which awarded Weidman "Knockout of the Night" honors. After the fight, Weidman expressed a desire to fight Anderson Silva and become the middleweight title holder.


title: Chris Weidman

text: Weidman was expected to fight Tim Boetsch on December 29, 2012, at UFC 155. However, Weidman pulled out of the bout due to an injury and was replaced by Costas Philippou.


title: Chris Weidman

text: After nearly a year out of competition due to injury and Hurricane Sandy, on July 6, 2013, Weidman faced Anderson Silva for the UFC Middleweight title in UFC 162 before a crowd of 12,399 spectators at the MGM Grand Garden Arena. Bookmakers rated Weidman a 2–1 underdog; however, numerous pundits and fighters including long-reigning UFC welterweight champion Georges St-Pierre, picked Weidman to upset the long-reigning middleweight champion:


title: Chris Weidman

text: I believe it's a bad matchup for Anderson Silva. Very bad, style-wise. Anderson's weaknesses are Weidman's strengths. I've trained with Weidman, and his wrestling is on another level. Not only is Chris Weidman going to beat Anderson Silva, I believe he's going to finish Anderson. I believe it's not going to last too long, this fight. This fight will shock a lot of people.


title: Chris Weidman

text: As St-Pierre predicted, Weidman knocked out Silva early in the second round with another "Knockout of the Night" performance to become the new UFC Middleweight Champion. In the first round, Weidman took down the champion onto the canvas to apply some solid ground-and-pound. The second round saw Silva taunting and mocking Weidman until he was caught and dropped by Weidman's left hook which was followed with punches to the grounded Silva — rendering him unconscious. The loss to Weidman was Silva's first in the UFC and ended his seven-year, 17-fight undefeated streak. The KO victory gave Weidman the distinction of being the first person to have ever knocked out Silva in a mixed martial arts match. In honor of Weidman's victory, Nassau County proclaimed July seventeenth "Chris Weidman Day". Mixed Martial Arts website Sherdog also declared Weidman's knockout of Anderson Silva as "Knockout of the Year" for 2013.


title: Chris Weidman

text: On July 13, 2013, the UFC President Dana White announced that Weidman would rematch Silva for his first title defense at UFC 168. Silva once again opened as the betting favorite.


title: Chris Weidman

text: At UFC 168 on December 28, 2013, Weidman defended his title against Anderson Silva. In contrast to their first fight in UFC 162, there was no overt showboating by Silva, yet Weidman still had Silva in trouble early in the first round by dropping him — while in the clinch — with a right hook to the side of the head — followed by a barrage of punches. In spite of Weidman's onslaught, Silva managed to pull guard, regain his composure and bloodied Weidman's nose with some elbows and hammer-fist punches off his back. Weidman, however, controlled the top position for the remainder of the round and landed punches and elbows. At the start of the second round, Silva attacked Weidman with a series of kicks including a heavy inside low kick which Weidman checked with his left knee. This check snapped Silva's left fibula and tibia on contact. Silva immediately fell to the mat, forcing referee Herb Dean to stop the fight 1:16 into the second round and give Weidman the victory by TKO. Low kicks were some of Silva's most effective strikes in their first encounter, which led Weidman to focus on defending against them for the rematch.


title: Chris Weidman

text: That was the number one thing I got hit with in the first fight, so I did work a lot against guys with good kicks and was working on checking them a lot. I did think that if he's going to go that hard on kicks, as he usually does, if I catch it on my knee it could really hurt him. But it's still crazy how that happened.


title: Chris Weidman

text: My trainer, Ray Longo, actually broke a guy's leg like that in the gym by putting the knee right on that shin when he kicked, just by following [the kick] up slowly, It's not really going shin-to-shin, but getting your knee on the shin. I've done it in sparring with some hard kickers to let them know not to kick me anymore. Their legs didn't break, but they would either take a minute to walk it off or they wouldn't be kicking me as much. It's something I've definitely been working on, thanks to Longo.


title: Chris Weidman

text: Weidman was expected to defend his belt against Vitor Belfort at UFC 173. Weidman opened as a 2-to-1 betting favorite. After Vitor Belfort withdrew from his title bout at UFC 173, it was announced that Lyoto Machida will next face Weidman. However, the bout was delayed after Weidman sustained a knee injury which required a minor surgery on both of his knees, including meniscal tears in both knees that he had since high school. The bout against Machida eventually took place on July 5, 2014, at UFC 175. Weidman retained his title, winning via unanimous decision (49–45, 48–47, and 49–46). After the fight his wife entered the octagon to kiss Weidman, whilst the audience cheered. The bout also earned Weidman his first "Fight of the Night" bonus award.


title: Chris Weidman

text: A rescheduled bout with Belfort was expected to take place on December 6, 2014, at UFC 181. However, on September 22, it was announced that Weidman had suffered a broken hand and the bout was again rescheduled to take place on February 28, 2015, at UFC 184. However, on January 30, the UFC announced that Weidman had pulled out of the bout, citing an injury he sustained in training. The bout with Belfort eventually took place on May 23, 2015, at UFC 187. After surviving an initial flurry of punches from Belfort, Weidman secured a takedown, went into the mount position, and won the fight via TKO due to strikes in the first round.


title: Chris Weidman

text: In the fourth defense of his title, Weidman faced Luke Rockhold on December 12, 2015, in the co-main event at UFC 194. Weidman lost the bout and his title via TKO in the fourth round. That was the very first defeat of Weidman's career. After two and a half back-and-forth rounds, Weidman conceded a takedown after a missed wheel kick, Rockhold took Weidman's back and from there transitioned to the full mount landing heavy damage with ground and pound. After taking damage Weidman survived until the fourth round where Rockhold again took him down and continued his ground and pound success which ultimately led to a fourth-round TKO stoppage by the referee Herb Dean. Both participants were awarded "Fight of the Night" honors.


title: Chris Weidman

text: A rematch with Rockhold was scheduled to take place on June 4, 2016, at UFC 199. However, Weidman pulled out of the fight on May 17 with a cervical disc herniation.


title: Chris Weidman

text: Weidman signed a new, six-fight contract with UFC in late September 2016 and faced Yoel Romero on November 12, 2016, at UFC 205. Weidman lost the fight in the third round after getting knocked out by a flying knee.


title: Chris Weidman

text: Weidman faced Gegard Mousasi at UFC 210. At 3:13 in the second round, Mousasi kneed Weidman twice in the head while Weidman had his hands near the ground. The referee stopped the fight because he thought that the second of these strikes were illegal. Weidman was allowed to recover, but after watching the replay the officials concluded the strike was legal. The doctors did not allow Weidman to continue and a TKO victory was granted to Mousasi.


title: Chris Weidman

text: Weidman next faced Kelvin Gastelum on July 22, 2017, at UFC on Fox 25. After being dropped at the end of the first round, Weidman rallied and submitted Gastelum via arm-triangle choke in the third round. Weidman appeared emotional and said at the post-fight press conference that the doubts and negative comments which he received during his three-fight losing streak were tough on him and his family and he was happy to be back in the game.


title: Chris Weidman

text: After the last debacle in the last fight. I had to sit back and listen to people doubt me and wait my turn to get back out here and show everybody what I'm made out of and man! I love my wife, I love my wife. Ah, this is a tough sport guys. This is a tough sport. You gotta have thick skin. The family has to have thick skin. Your coaches have to have thick skin. You drag your family through mud in this sport with the things that they have to hear. Feels good to get back where I deserve.


title: Chris Weidman

text: A rematch with Luke Rockhold was expected to take place on November 3, 2018 at UFC 230. However, on October 19, 2018, it was reported Rockhold withdrew from the bout, citing an injury, and he was replaced by Ronaldo Souza. Weidman lost the back-and-forth bout via KO at 2:12 of the third round. Both fighters earned Fight of the Night honors.


title: Chris Weidman

text: In June 2019, Weidman announced his intentions to move up to Light Heavyweight beginning later on in 2019. He cites numerous surgeries which prevent him from being able to cut to Middleweight as his reason for moving up weight classes.


title: Chris Weidman

text: Weidman's light heavyweight debut took place on October 18, 2019 at UFC on ESPN 6 against Dominick Reyes in the main event. Weidman lost the fight via knockout in the first round.


title: Chris Weidman

text: Weidman was expected to face Jack Hermansson in a middleweight bout on May 2, 2020 at . However, on April 9, Dana White, the president of UFC announced that this event was postponed to a future date and the pairing was scrapped.


title: Chris Weidman

text: Weidman faced Omari Akhmedov on August 8, 2020 at UFC Fight Night 174. He won the fight via unanimous decision.


title: Chris Weidman

text: A rematch with Uriah Hall was expected to take place on February 13, 2021 at UFC 258. However, Weidman was pulled from the event due to a positive COVID-19 test and the bout was cancelled, The rematch took place at UFC 261 on April 24, 2021. At the start of the first round, Weidman threw a heavy outside low kick which Hall checked with his left knee, causing Weidman's right fibula and tibia to snap on contact. Weidman immediately fell to the mat, with referee Herb Dean calling a stop to the fight and declaring Hall the winner via technical knockout. This injury was similar to the one Anderson Silva sustained against Weidman during their second match in December 2013, when Silva's left fibula and tibia were snapped after Weidman checked a leg kick.


title: Chris Weidman

text: After the injury at UFC 261, Weidman was stretchered out of the octagon and was transported to the hospital, where he underwent surgery. He announced the following day that doctors had informed him that he would be unable to walk without crutches for eight weeks, and would need a recovery period of between six and twelve months before he could resume mixed martial arts training. As of mid-June, he had already returned to light training within seven weeks after sustaining the injury. Weidman then underwent a second surgery as the fracture was not healing properly. As of early 2022, Weidman hoped to have a fight scheduled before the end of the year.


title: Chris Weidman

text: On October 29, 2012, Weidman's house was severely damaged by Hurricane Sandy. He subsequently volunteered to help rebuild Sandy victims' homes via the non-profit group Staten Strong. Weidman is a practicing Christian. He and his wife Marivi have three children: Cassidy, CJ, and Colten. The couple began dating during their high school days. Weidman and his family moved from New York to South Carolina in the summer of 2020.


title: Directed-energy weapon

text: A directed-energy weapon (DEW) is a ranged weapon that damages its target with highly focused energy without a solid projectile, including lasers, microwaves, particle beams, and sound beams. Potential applications of this technology include weapons that target personnel, missiles, vehicles, and optical devices. In the United States, the Pentagon, DARPA, the Air Force Research Laboratory, United States Army Armament Research Development and Engineering Center, and the Naval Research Laboratory are researching directed-energy weapons to counter ballistic missiles, hypersonic cruise missiles, and hypersonic glide vehicles. These systems of missile defense are expected to come online no sooner than the mid to late-2020s.


title: Directed-energy weapon

text: China, France, Germany, the United Kingdom, Russia, India, and Pakistan are also developing military-grade directed-energy weapons, while Iran and Turkey claim to have them in active service. The first use of directed-energy weapons in combat between military forces was claimed to have occurred in Libya in August 2019 by Turkey, which claimed to use the ALKA directed-energy weapon. After decades of research and development, most directed-energy weapons are still at the experimental stage and it remains to be seen if or when they will be deployed as practical, high-performance military weapons.


title: Directed-energy weapon

text: Some devices are described as microwave weapons; the microwave range is commonly defined as being between 300 MHz and 300 GHz (wavelengths of 1 meter to 1 millimeter), which is within the radiofrequency (RF) range. Some examples of weapons which have been publicized by the military are as follows:


title: Directed-energy weapon

text: Active Denial System is a millimeter wave source that heats the water in a human target's skin and thus causes incapacitating pain. It was developed by the U.S. Air Force Research Laboratory and Raytheon for riot-control duty. Though intended to cause severe pain while leaving no lasting damage, concern has been voiced as to whether the system could cause irreversible damage to the eyes. There has yet to be testing for long-term side effects of exposure to the microwave beam. It can also destroy unshielded electronics. The device comes in various sizes, including attached to a Humvee.


title: Directed-energy weapon

text: Vigilant Eagle is a ground-based airport defense system that directs high-frequency microwaves towards any projectile that is fired at an aircraft. It was announced by Raytheon in 2005, and the effectiveness of its waveforms was reported to have been demonstrated in field tests to be highly effective in defeating MANPADS missiles.


title: Directed-energy weapon

text: The system consists of a missile-detecting and tracking subsystem (MDT), a command and control system, and a scanning array. The MDT is a fixed grid of passive infrared (IR) cameras. The command and control system determines the missile launch point. The scanning array projects microwaves that disrupt the surface-to-air missile's guidance system, deflecting it from the aircraft. Vigilant Eagle was not mentioned on Raytheon's Web site in 2022.


title: Directed-energy weapon

text: Bofors HPM Blackout is a high-powered microwave weapon that is said to be able to destroy at short distance a wide variety of commercial off-the-shelf (COTS) electronic equipment and is purportedly non-lethal.


title: Directed-energy weapon

text: The effective radiated power (ERP) of the EL/M-2080 Green Pine radar makes it a hypothetical candidate for conversion into a directed-energy weapon, by focusing pulses of radar energy on target missiles. The energy spikes are tailored to enter missiles through antennas or sensor apertures where they can fool guidance systems, scramble computer memories or even burn out sensitive electronic components.


title: Directed-energy weapon

text: AESA radars mounted on fighter aircraft have been slated as directed energy weapons against missiles, however, a senior US Air Force officer noted: "they aren't particularly suited to create weapons effects on missiles because of limited antenna size, power and field of view". Potentially lethal effects are produced only inside 100 meters range, and disruptive effects at distances on the order of one kilometer. Moreover, cheap countermeasures can be applied to existing missiles.


title: Directed-energy weapon

text: A weapon often described as an "anti-drone rifle" or "anti-drone gun" is a battery-powered electromagnetic pulse weapon held to an operator's shoulder, pointed at a flying target in a way similar to a rifle, and operated. While not a rifle or gun, it is so nicknamed as it is handled in the same way as a personal rifle. The device emits separate electromagnetic pulses to suppress navigation and transmission channels used to operate an aerial drone, terminating the drone's contact with its operator; the out-of-control drone then crashes.


title: Directed-energy weapon

text: The Russian "Stupor" is reported to have a range of two kilometers, covering a 20-degree sector; it also suppresses the drone's cameras. "Stupor" is reported to have been used by Russian forces during the Russian military intervention in the Syrian civil war.


title: Directed-energy weapon

text: Both Russia and Ukraine are reported to use these devices during the 2022 Russian invasion of Ukraine.


title: Directed-energy weapon

text: The Ukrainian army are reported to use the Ukrainian KVS G-6, with a 3.5 km range and able to operate continuously for 30 minutes. The manufacturer states that the weapon can disrupt remote control, the transmission of video at 2.4 and 5 GHz, and GPS and Glonass satellite navigation signals.


title: Directed-energy weapon

text: Particle-beam weapons can use charged or neutral particles, and can be either endoatmospheric or exoatmospheric. Particle beams as beam weapons are theoretically possible, but practical weapons have not been demonstrated yet. Certain types of particle beams have the advantage of being self-focusing in the atmosphere.


title: Directed-energy weapon

text: Blooming is also a problem in particle-beam weapons. Energy that would otherwise be focused on the target spreads out and the beam becomes less effective:


title: Directed-energy weapon

text: Plasma weapons fire a beam, bolt, or stream of plasma, which is an excited state of matter consisting of atomic electrons & nuclei and free electrons if ionized, or other particles if pinched.


title: Directed-energy weapon

text: The MARAUDER ("Magnetically Accelerated Ring to Achieve Ultra-high Directed-Energy and Radiation") used the Shiva Star project (a high energy capacitor bank which provided the means to test weapons and other devices requiring brief and extremely large amounts of energy) to accelerate a toroid of plasma at a significant percentage of the speed of light.


title: Directed-energy weapon

text: The Long Range Acoustic Device (LRAD) is an acoustic hailing device developed by Genasys (formerly LRAD Corporation) to send messages and warning tones over longer distances or at higher volume than normal loudspeakers, and as a non-lethal directed-acoustic-energy weapon. LRAD systems are used for long-range communications in a variety of applications and as a means of non-lethal, non-projectile crowd control. They are also used on ships as an anti-piracy measure.


title: Directed-energy weapon

text: According to the manufacturer's specifications, the systems weigh from and can emit sound in a 30°- 60° beam at 2.5 kHz. They range in size from small, portable handheld units which can be strapped to a person's chest, to larger models which require a mount. The power of the sound beam which LRADs produce is sufficient to penetrate vehicles and buildings while retaining a high degree of fidelity, so that verbal messages can be conveyed clearly in some situations. Their weapons capability has been controversially used in the USA to disrupt numerous protests.


title: Directed-energy weapon

text: According to a legend, Archimedes created a mirror with an adjustable focal length (or more likely, a series of mirrors focused on a common point) to focus sunlight on ships of the Roman fleet as they invaded Syracuse, setting them on fire. Historians point out that the earliest accounts of the battle did not mention a "burning mirror", but merely stated that Archimedes's ingenuity combined with a way to hurl fire were relevant to the victory. Some attempts to replicate this feat have had some success; in particular, an experiment by students at MIT showed that a mirror-based weapon was at least possible, if not necessarily practical. The hosts of "MythBusters" tackled the Mirrors of Archimedes three times (in episodes 19, 57 and 172) and were never able to make the target ship catch fire, declaring the myth busted three separate times.


title: Directed-energy weapon

text: In 1935, the British Air Ministry asked Robert Watson-Watt of the Radio Research Station whether a "death ray" was possible. He and colleague Arnold Wilkins quickly concluded that it was not feasible, but as a consequence suggested using radio for the detection of aircraft and this started the development of radar in Britain.


title: Directed-energy weapon

text: Stories in the 1930s and World War Two gave rise to the idea of an "engine-stopping ray". They seemed to have arisen from the testing of the television transmitter in Feldberg, Germany. Because electrical noise from car engines would interfere with field strength measurements, sentries would stop all traffic in the vicinity for the twenty minutes or so needed for a test. Reversing the order of events in retelling the story created a "tale" where tourists car engine stopped first and then were approached by a German soldier who told them that they had to wait. The soldier returned a short time later to say that the engine would now work and the tourists drove off. Such stories were circulating in Britain around 1938 and during the war British Intelligence relaunched the myth as a "British engine-stopping ray," trying to spoof the Germans into researching what the British had supposedly invented in an attempt to tie up German scientific resources.


title: Directed-energy weapon

text: During the early 1940s Axis engineers developed a sonic cannon that could cause fatal vibrations in its target body. A methane gas combustion chamber leading to two parabolic dishes pulse-detonated at roughly 44 Hz. This sound, magnified by the dish reflectors, caused vertigo and nausea at by vibrating the middle ear bones and shaking the cochlear fluid within the inner ear. At distances of , the sound waves could act on organ tissues and fluids by repeatedly compressing and releasing compressive resistant organs such as the kidneys, spleen, and liver. (It had little detectable effect on malleable organs such as the heart, stomach and intestines.) Lung tissue was affected at only the closest ranges as atmospheric air is highly compressible and only the blood rich alveoli resist compression. In practice, the weapon was highly vulnerable to enemy fire. Rifle, bazooka and mortar rounds easily deformed the parabolic reflectors, rendering the wave amplification ineffective.


title: Directed-energy weapon

text: In the later phases of World War II, Nazi Germany increasingly put its hopes on research into technologically revolutionary secret weapons, the "Wunderwaffe".


title: Directed-energy weapon

text: Among the directed-energy weapons the Nazis investigated were X-ray beam weapons developed under Heinz Schmellenmeier, Richard Gans and Fritz Houtermans. They built an electron accelerator called Rheotron to generate hard X-ray synchrotron beams for the Reichsluftfahrtministerium (RLM). (Invented by Max Steenbeck at Siemens-Schuckert in the 1930s, these were later called Betatrons by the Americans.) The intent was to pre-ionize ignition in aircraft engines and hence serve as anti-aircraft DEW and bring planes down into the reach of the flak. The Rheotron was captured by the Americans in Burggrub on April 14, 1945.


title: Directed-energy weapon

text: Another approach was Ernst Schiebolds 'Röntgenkanone' developed from 1943 in Großostheim near Aschaffenburg. Richert Seifert & Co from Hamburg delivered parts.


title: Directed-energy weapon

text: The Central Intelligence Agency informed Secretary Henry Kissinger that it had twelve reports of Soviet forces using laser weapons against Chinese forces during the 1969 Sino-Soviet border clashes, though William Colby doubted that they had actually been employed.


title: Directed-energy weapon

text: In 1973, "New Scientist" magazine reported that a sonic weapon known as a 'squawk box' underwent successful field trials in Northern Ireland, using soldiers as guinea pigs. The device combined two slightly different frequencies which when heard would be heard as the sum of the two frequencies (ultrasonic) and the difference between the two frequencies (infrasonic) e.g. two directional speakers emitting 16,000 Hz and 16,002 Hz frequencies would produce in the ear two frequencies of 32,002 Hz and 2 Hz. The article states: 'The squawk box is highly directional which gives it its appeal. Its effective beam width is so small that it can be directed at individuals in a riot. Other members of a crowd are unaffected, except by panic when they see people fainting, being sick, or running from the scene with their hands over their ears. The virtual inaudibility of the equipment is said to produce a "spooky" psychological effect.' The British Ministry of Defence denied the existence of such a device. It stated that it did have, however, an 'ultra-loud public address system which [...] could be "used for verbal communication over two miles, or put out a sustained or modulated sound blanket to make conversation, and thus crowd organisation, impossible."'


title: Directed-energy weapon

text: In East Germany in the 1960s, many people were arrested and interrogated for holding politically incorrect views or for performing actions deemed hostile by the ruling socialist state. Such arrests, which could also involve direct physical torture, were condemned internationally. In an effort to avoid such condemnation the state security service, the Stasi, attempted alternative methods of repression which could paralyze people without keeping them in a physical prison. They could therefore avoid there being any evidence of repression or at least limit it. One such alternative method was called decomposition (transl. Zersetzung). In the 1970s and '80s it became the primary method of repressing domestic 'hostile-negative' forces. It was a psychological warfare method which could involve the group based and systematic gaslighting of targets, among other things. Some of the victims of this method suffered from suspicious cases of cancer and have claimed that they had also been targeted with directed X-rays. In addition, when the East German state collapsed powerful X-ray equipment was found in prisons without there being any apparent reason to justify its presence. In 1999, the modern German state was investigating the possibility that this X-ray equipment was being used as weaponry and that it was a deliberate policy of the Stasi to attempt to give prisoners radiation poisoning, and thereby cancer, through the use of directed X-rays. The negative effects of the radiation poisoning and cancer would extend past the period of incarceration. In this manner someone could be debilitated even though they were no longer imprisoned. The historian Mary Fulbrook states, "The subsequent serious illnesses and premature deaths of dissidents such as the novelist Jürgen Fuchs, and the author of the critical analysis of 'The Alternative in Eastern Europe', Rudolf Bahro, have been linked by some to the suspicion of exposure to extraordinarily high and sustained levels of X-rays while waiting for interrogations, and being strapped to unpleasant chairs in small prison cells in front of mysterious closed boxes- boxes that, along with their mysterious apparatus, curiously disappeared after the collapse of the SED (Socialist Unity Party of Germany) system."


title: Directed-energy weapon

text: In the 1980s, U.S. President Ronald Reagan proposed the Strategic Defense Initiative (SDI) program, which was nicknamed "Star Wars". It suggested that lasers, perhaps space-based X-ray lasers, could destroy ICBMs in flight. Panel discussions on the role of high-power lasers in SDI took place at various laser conferences, during the 1980s, with the participation of noted physicists including Edward Teller.


title: Directed-energy weapon

text: Though the strategic missile defense concept has continued to the present under the Missile Defense Agency, most of the directed-energy weapon concepts were shelved. However, Boeing has been somewhat successful with the Boeing YAL-1 and Boeing NC-135, the first of which destroyed two missiles in February 2010. Funding has been cut to both of the programs.


title: Directed-energy weapon

text: During the Iraq War, electromagnetic weapons, including high power microwaves, were used by the U.S. military to disrupt and destroy Iraqi electronic systems and may have been used for crowd control. Types and magnitudes of exposure to electromagnetic fields are unknown.


title: Directed-energy weapon

text: The Soviet Union invested some effort in the development of ruby and carbon dioxide lasers as anti-ballistic missile systems, and later as a tracking and anti-satellite system. There are reports that the Terra-3 complex at Sary Shagan was used on several occasions to temporarily "blind" US spy satellites in the IR range.


title: Directed-energy weapon

text: It has been claimed that the USSR made use of the lasers at the Terra-3 site to target the Space Shuttle "Challenger" in 1984. At the time, the Soviet Union was concerned that the shuttle was being used as a reconnaissance platform. On 10 October 1984 (STS-41-G), the Terra-3 tracking laser was allegedly aimed at "Challenger" as it passed over the facility. Early reports claimed that this was responsible for causing "malfunctions on the space shuttle and distress to the crew", and that the United States filed a diplomatic protest about the incident. However, this story is comprehensively denied by the crew members of STS-41-G and knowledgeable members of the US intelligence community. After the end of the Cold War, the Terra-3 facility was found to be a low-power laser testing site with limited satellite tracking capabilities, which is now abandoned and partially disassembled.


title: Directed-energy weapon

text: Havana syndrome is a set of medical symptoms reported by US personnel in Havana, Cuba and other locations, suspected by the National Academies of Sciences, Engineering, and Medicine to be caused by microwave energy.


title: Directed-energy weapon

text: LRADs are often fitted on commercial and military ships. They have been used on several occasions to repel pirate attacks by sending warnings and by producing intolerable levels of sound. For example, in 2005 the cruise liner "Seabourn Spirit" used a sonic weapon to defend itself from Somali pirates in the Indian ocean. A few years later, the cruise liner "Spirit of Adventure" also defended itself from Somali pirates by using its LRAD to force them to retreat.


title: Directed-energy weapon

text: The TECOM Technology Symposium in 1997 concluded on non-lethal weapons, "determining the target effects on personnel is the greatest challenge to the testing community", primarily because "the potential of injury and death severely limits human tests".


title: Directed-energy weapon

text: Also, "directed-energy weapons that target the central nervous system and cause neurophysiological disorders may violate the Certain Conventional Weapons Convention of 1980. Weapons that go beyond non-lethal intentions and cause 'superfluous injury or unnecessary suffering' may also violate the Protocol I to the Geneva Conventions of 1977."


title: Directed-energy weapon

text: Light and repetitive visual signals can induce epileptic seizures. Vection and motion sickness can also occur.


title: Castle

text: A castle is a type of fortified structure built during the Middle Ages predominantly by the nobility or royalty and by military orders. Scholars debate the scope of the word "castle", but usually consider it to be the private fortified residence of a lord or noble. This is distinct from a palace, which is not fortified;


title: Castle

text: from a fortress, which was not always a residence for royalty or nobility; from a "pleasance" which was a walled-in residence for nobility, but not adequately fortified;


title: Castle

text: and from a fortified settlement, which was a public defence – though there are many similarities among these types of construction. Use of the term has varied over time and has also been applied to structures such as hill forts and 19th-20th century homes built to resemble castles. Over the approximately 900 years when genuine castles were built, they took on a great many forms with many different features, although some, such as curtain walls, arrowslits, and portcullises, were commonplace.


title: Castle

text: European-style castles originated in the 9th and 10th centuries, after the fall of the Carolingian Empire resulted in its territory being divided among individual lords and princes. These nobles built castles to control the area immediately surrounding them and the castles were both offensive and defensive structures; they provided a base from which raids could be launched as well as offered protection from enemies. Although their military origins are often emphasised in castle studies, the structures also served as centres of administration and symbols of power. Urban castles were used to control the local populace and important travel routes, and rural castles were often situated near features that were integral to life in the community, such as mills, fertile land, or a water source.


title: Castle

text: Many northern European castles were originally built from earth and timber, but had their defences replaced later by stone. Early castles often exploited natural defences, lacking features such as towers and arrowslits and relying on a central keep. In the late 12th and early 13th centuries, a scientific approach to castle defence emerged. This led to the proliferation of towers, with an emphasis on flanking fire. Many new castles were polygonal or relied on concentric defence – several stages of defence within each other that could all function at the same time to maximise the castle's firepower. These changes in defence have been attributed to a mixture of castle technology from the Crusades, such as concentric fortification, and inspiration from earlier defences, such as Roman forts. Not all the elements of castle architecture were military in nature, so that devices such as moats evolved from their original purpose of defence into symbols of power. Some grand castles had long winding approaches intended to impress and dominate their landscape.


title: Castle

text: Although gunpowder was introduced to Europe in the 14th century, it did not significantly affect castle building until the 15th century, when artillery became powerful enough to break through stone walls. While castles continued to be built well into the 16th century, new techniques to deal with improved cannon fire made them uncomfortable and undesirable places to live. As a result, true castles went into decline and were replaced by artillery forts with no role in civil administration, and country houses that were indefensible. From the 18th century onwards, there was a renewed interest in castles with the construction of mock castles, part of a romantic revival of Gothic architecture, but they had no military purpose.


title: Castle

text: The word "castle" is derived from the Latin word "castellum", which is a diminutive of the word "castrum", meaning "fortified place". The Old English "castel", Occitan "castel" or "chastel", French "château", Spanish "castillo", Portuguese "castelo", Italian "castello", and a number of words in other languages also derive from "castellum". The word "castle" was introduced into English shortly before the Norman Conquest to denote this type of building, which was then new to England.


title: Castle

text: In its simplest terms, the definition of a castle accepted amongst academics is "a private fortified residence". This contrasts with earlier fortifications, such as Anglo-Saxon burhs and walled cities such as Constantinople and Antioch in the Middle East; castles were not communal defences but were built and owned by the local feudal lords, either for themselves or for their monarch. Feudalism was the link between a lord and his vassal where, in return for military service and the expectation of loyalty, the lord would grant the vassal land. In the late 20th century, there was a trend to refine the definition of a castle by including the criterion of feudal ownership, thus tying castles to the medieval period; however, this does not necessarily reflect the terminology used in the medieval period. During the First Crusade (1096–1099), the Frankish armies encountered walled settlements and forts that they indiscriminately referred to as castles, but which would not be considered as such under the modern definition.


title: Castle

text: Castles served a range of purposes, the most important of which were military, administrative, and domestic. As well as defensive structures, castles were also offensive tools which could be used as a base of operations in enemy territory. Castles were established by Norman invaders of England for both defensive purposes and to pacify the country's inhabitants. As William the Conqueror advanced through England, he fortified key positions to secure the land he had taken. Between 1066 and 1087, he established 36 castles such as Warwick Castle, which he used to guard against rebellion in the English Midlands.


title: Castle

text: Towards the end of the Middle Ages, castles tended to lose their military significance due to the advent of powerful cannons and permanent artillery fortifications; as a result, castles became more important as residences and statements of power. A castle could act as a stronghold and prison but was also a place where a knight or lord could entertain his peers. Over time the aesthetics of the design became more important, as the castle's appearance and size began to reflect the prestige and power of its occupant. Comfortable homes were often fashioned within their fortified walls. Although castles still provided protection from low levels of violence in later periods, eventually they were succeeded by country houses as high status residences.


title: Castle

text: "Castle" is sometimes used as a catch-all term for all kinds of fortifications and, as a result, has been misapplied in the technical sense. An example of this is Maiden Castle which, despite the name, is an Iron Age hill fort which had a very different origin and purpose.


title: Castle

text: Although "castle" has not become a generic term for a manor house (like château in French and Schloss in German), many manor houses contain "castle" in their name while having few if any of the architectural characteristics, usually as their owners liked to maintain a link to the past and felt the term "castle" was a masculine expression of their power. In scholarship the castle, as defined above, is generally accepted as a coherent concept, originating in Europe and later spreading to parts of the Middle East, where they were introduced by European Crusaders. This coherent group shared a common origin, dealt with a particular mode of warfare, and exchanged influences.


title: Castle

text: In different areas of the world, analogous structures shared features of fortification and other defining characteristics associated with the concept of a castle, though they originated in different periods and circumstances and experienced differing evolutions and influences. For example, "shiro" in Japan, described as castles by historian Stephen Turnbull, underwent "a completely different developmental history, were built in a completely different way and were designed to withstand attacks of a completely different nature". While European castles built from the late 12th and early 13th century onwards were generally stone, "shiro" were predominantly timber buildings into the 16th century.


title: Castle

text: By the 16th century, when Japanese and European cultures met, fortification in Europe had moved beyond castles and relied on innovations such as the Italian "trace italienne" and star forts. Forts in India present a similar case; when they were encountered by the British in the 17th century, castles in Europe had generally fallen out of use militarily. Like "shiro", the Indian forts, "durga" or "durg" in Sanskrit, shared features with castles in Europe such as acting as a domicile for a lord as well as being fortifications. They too developed differently from the structures known as castles that had their origins in Europe.


title: Castle

text: A motte was an earthen mound with a flat top. It was often artificial, although sometimes it incorporated a pre-existing feature of the landscape. The excavation of earth to make the mound left a ditch around the motte, called a moat (which could be either wet or dry). Although the motte is commonly associated with the bailey to form a motte-and-bailey castle, this was not always the case and there are instances where a motte existed on its own.


title: Castle

text: "Motte" refers to the mound alone, but it was often surmounted by a fortified structure, such as a keep, and the flat top would be surrounded by a palisade. It was common for the motte to be reached over a flying bridge (a bridge over the ditch from the counterscarp of the ditch to the edge of the top of the mound), as shown in the Bayeux Tapestry's depiction of Château de Dinan. Sometimes a motte covered an older castle or hall, whose rooms became underground storage areas and prisons beneath a new keep.


title: Castle

text: A bailey, also called a ward, was a fortified enclosure. It was a common feature of castles, and most had at least one. The keep on top of the motte was the domicile of the lord in charge of the castle and a bastion of last defence, while the bailey was the home of the rest of the lord's household and gave them protection. The barracks for the garrison, stables, workshops, and storage facilities were often found in the bailey. Water was supplied by a well or cistern. Over time the focus of high status accommodation shifted from the keep to the bailey; this resulted in the creation of another bailey that separated the high status buildings – such as the lord's chambers and the chapel – from the everyday structures such as the workshops and barracks.


title: Castle

text: From the late 12th century there was a trend for knights to move out of the small houses they had previously occupied within the bailey to live in fortified houses in the countryside. Although often associated with the motte-and-bailey type of castle, baileys could also be found as independent defensive structures. These simple fortifications were called ringworks. The enceinte was the castle's main defensive enclosure, and the terms "bailey" and "enceinte" are linked. A castle could have several baileys but only one enceinte. Castles with no keep, which relied on their outer defences for protection, are sometimes called enceinte castles; these were the earliest form of castles, before the keep was introduced in the 10th century.


title: Castle

text: A keep was a great tower and usually the most strongly defended point of a castle before the introduction of concentric defence. "Keep" was not a term used in the medieval period – the term was applied from the 16th century onwards – instead "donjon" was used to refer to great towers, or "turris" in Latin. In motte-and-bailey castles, the keep was on top of the motte. "Dungeon" is a corrupted form of "donjon" and means a dark, unwelcoming prison. Although often the strongest part of a castle and a last place of refuge if the outer defences fell, the keep was not left empty in case of attack but was used as a residence by the lord who owned the castle, or his guests or representatives.


title: Castle

text: At first this was usual only in England, when after the Norman Conquest of 1066 the "conquerors lived for a long time in a constant state of alert"; elsewhere the lord's wife presided over a separate residence ("domus", "aula" or "mansio" in Latin) close to the keep, and the donjon was a barracks and headquarters. Gradually, the two functions merged into the same building, and the highest residential storeys had large windows; as a result for many structures, it is difficult to find an appropriate term. The massive internal spaces seen in many surviving donjons can be misleading; they would have been divided into several rooms by light partitions, as in a modern office building. Even in some large castles the great hall was separated only by a partition from the lord's "chamber", his bedroom and to some extent his office.


title: Castle

text: Curtain walls were defensive walls enclosing a bailey. They had to be high enough to make scaling the walls with ladders difficult and thick enough to withstand bombardment from siege engines which, from the 15th century onwards, included gunpowder artillery. A typical wall could be thick and tall, although sizes varied greatly between castles. To protect them from undermining, curtain walls were sometimes given a stone skirt around their bases. Walkways along the tops of the curtain walls allowed defenders to rain missiles on enemies below, and battlements gave them further protection. Curtain walls were studded with towers to allow enfilading fire along the wall. Arrowslits in the walls did not become common in Europe until the 13th century, for fear that they might compromise the wall's strength.


title: Castle

text: The entrance was often the weakest part in a circuit of defences. To overcome this, the gatehouse was developed, allowing those inside the castle to control the flow of traffic. In earth and timber castles, the gateway was usually the first feature to be rebuilt in stone. The front of the gateway was a blind spot and to overcome this, projecting towers were added on each side of the gate in a style similar to that developed by the Romans. The gatehouse contained a series of defences to make a direct assault more difficult than battering down a simple gate. Typically, there were one or more portcullises – a wooden grille reinforced with metal to block a passage – and arrowslits to allow defenders to harry the enemy. The passage through the gatehouse was lengthened to increase the amount of time an assailant had to spend under fire in a confined space and unable to retaliate.


title: Castle

text: It is a popular myth that so-called murder holes – openings in the ceiling of the gateway passage – were used to pour boiling oil or molten lead on attackers; the price of oil and lead and the distance of the gatehouse from fires meant that this was impractical. This method was, however, a common practice in the MENA region and the Mediterranean castles and fortifications where such resources were abundant. They were most likely used to drop objects on attackers, or to allow water to be poured on fires to extinguish them. Provision was made in the upper storey of the gatehouse for accommodation so the gate was never left undefended, although this arrangement later evolved to become more comfortable at the expense of defence.


title: Castle

text: During the 13th and 14th centuries the barbican was developed. This consisted of a rampart, ditch, and possibly a tower, in front of the gatehouse which could be used to further protect the entrance. The purpose of a barbican was not just to provide another line of defence but also to dictate the only approach to the gate.


title: Castle

text: A moat was a ditch surrounding a castle – or dividing one part of a castle from another – and could be either dry or filled with water. Its purpose often had a defensive purpose, preventing siege towers from reaching walls making mining harder, but could also be ornamental. Water moats were found in low-lying areas and were usually crossed by a drawbridge, although these were often replaced by stone bridges. The site of the 13th-century Caerphilly Castle in Wales covers over and the water defences, created by flooding the valley to the south of the castle, are some of the largest in Western Europe.


title: Castle

text: Battlements were most often found surmounting curtain walls and the tops of gatehouses, and comprised several elements: crenellations, hoardings, machicolations, and loopholes. Crenellation is the collective name for alternating crenels and merlons: gaps and solid blocks on top of a wall. Hoardings were wooden constructs that projected beyond the wall, allowing defenders to shoot at, or drop objects on, attackers at the base of the wall without having to lean perilously over the crenellations, thereby exposing themselves to retaliatory fire. Machicolations were stone projections on top of a wall with openings that allowed objects to be dropped on an enemy at the base of the wall in a similar fashion to hoardings.


title: Castle

text: Arrowslits, also commonly called loopholes, were narrow vertical openings in defensive walls which allowed arrows or crossbow bolts to be fired on attackers. The narrow slits were intended to protect the defender by providing a very small target, but the size of the opening could also impede the defender if it was too small. A smaller horizontal opening could be added to give an archer a better view for aiming. Sometimes a sally port was included; this could allow the garrison to leave the castle and engage besieging forces. It was usual for the latrines to empty down the external walls of a castle and into the surrounding ditch.


title: Castle

text: A postern is a secondary door or gate in a concealed location, usually in a fortification such as a city wall.


title: Castle

text: The great hall was a large, decorated room where a lord received his guests. The hall represented the prestige, authority, and richness of the lord. Events such as feasts, banquets, social or ceremonial gatherings, meetings of the military council, and judicial trials were held in the great hall. Sometimes the great hall existed as a separate building, in that case, it was called a hall-house.


title: Castle

text: Historian Charles Coulson states that the accumulation of wealth and resources, such as food, led to the need for defensive structures. The earliest fortifications originated in the Fertile Crescent, the Indus Valley, Europe, Egypt, and China where settlements were protected by large walls. In Northern Europe hill forts were first developed in the Bronze Age, which then proliferated across Europe in the Iron Age. Hillforts in Britain typically used earthworks rather than stone as a building material. Many earthworks survive today, along with evidence of palisades to accompany the ditches. In central and western Europe, oppida emerged in the 2nd century BC; these were densely inhabited fortified settlements, such as the oppidum of Manching. Some oppida walls were built on a massive scale, utilising stone, wood, iron and earth in their construction. The Romans encountered fortified settlements such as hill forts and oppida when expanding their territory into northern Europe. Their defences were often effective, and were only overcome by the extensive use of siege engines and other siege warfare techniques, such as at the Battle of Alesia. The Romans' own fortifications ("castra") varied from simple temporary earthworks thrown up by armies on the move, to elaborate permanent stone constructions, notably the milecastles of Hadrian's Wall. Roman forts were generally rectangular with rounded corners – a "playing-card shape".


title: Castle

text: In the medieval period, castles were influenced by earlier forms of elite architecture, contributing to regional variations. Importantly, while castles had military aspects, they contained a recognisable household structure within their walls, reflecting the multi-functional use of these buildings.


title: Castle

text: The subject of the emergence of castles in Europe is a complex matter which has led to considerable debate. Discussions have typically attributed the rise of the castle to a reaction to attacks by Magyars, Muslims, and Vikings and a need for private defence. The breakdown of the Carolingian Empire led to the privatisation of government, and local lords assumed responsibility for the economy and justice. However, while castles proliferated in the 9th and 10th centuries the link between periods of insecurity and building fortifications is not always straightforward. Some high concentrations of castles occur in secure places, while some border regions had relatively few castles.


title: Castle

text: It is likely that the castle evolved from the practice of fortifying a lordly home. The greatest threat to a lord's home or hall was fire as it was usually a wooden structure. To protect against this, and keep other threats at bay, there were several courses of action available: create encircling earthworks to keep an enemy at a distance; build the hall in stone; or raise it up on an artificial mound, known as a motte, to present an obstacle to attackers. While the concept of ditches, ramparts, and stone walls as defensive measures is ancient, raising a motte is a medieval innovation.


title: Castle

text: A bank and ditch enclosure was a simple form of defence, and when found without an associated motte is called a ringwork; when the site was in use for a prolonged period, it was sometimes replaced by a more complex structure or enhanced by the addition of a stone curtain wall. Building the hall in stone did not necessarily make it immune to fire as it still had windows and a wooden door. This led to the elevation of windows to the second storey – to make it harder to throw objects in – and to move the entrance from ground level to the second storey. These features are seen in many surviving castle keeps, which were the more sophisticated version of halls. Castles were not just defensive sites but also enhanced a lord's control over his lands. They allowed the garrison to control the surrounding area, and formed a centre of administration, providing the lord with a place to hold court.


title: Castle

text: Building a castle sometimes required the permission of the king or other high authority. In 864 the King of West Francia, Charles the Bald, prohibited the construction of "castella" without his permission and ordered them all to be destroyed. This is perhaps the earliest reference to castles, though military historian R. Allen Brown points out that the word "castella" may have applied to any fortification at the time.


title: Castle

text: In some countries the monarch had little control over lords, or required the construction of new castles to aid in securing the land so was unconcerned about granting permission – as was the case in England in the aftermath of the Norman Conquest and the Holy Land during the Crusades. Switzerland is an extreme case of there being no state control over who built castles, and as a result there were 4,000 in the country. There are very few castles dated with certainty from the mid-9th century. Converted into a donjon around 950, Château de Doué-la-Fontaine in France is the oldest standing castle in Europe.


title: Castle

text: From 1000 onwards, references to castles in texts such as charters increased greatly. Historians have interpreted this as evidence of a sudden increase in the number of castles in Europe around this time; this has been supported by archaeological investigation which has dated the construction of castle sites through the examination of ceramics. The increase in Italy began in the 950s, with numbers of castles increasing by a factor of three to five every 50 years, whereas in other parts of Europe such as France and Spain the growth was slower. In 950 Provence was home to 12 castles, by 1000 this figure had risen to 30, and by 1030 it was over 100. Although the increase was slower in Spain, the 1020s saw a particular growth in the number of castles in the region, particularly in contested border areas between Christian and Muslim lands.


title: Castle

text: Despite the common period in which castles rose to prominence in Europe, their form and design varied from region to region. In the early 11th century, the motte and keep – an artificial mound with a palisade and tower on top – was the most common form of castle in Europe, everywhere except Scandinavia. While Britain, France, and Italy shared a tradition of timber construction that was continued in castle architecture, Spain more commonly used stone or mud-brick as the main building material.


title: Castle

text: The Muslim invasion of the Iberian Peninsula in the 8th century introduced a style of building developed in North Africa reliant on "tapial", pebbles in cement, where timber was in short supply. Although stone construction would later become common elsewhere, from the 11th century onwards it was the primary building material for Christian castles in Spain, while at the same time timber was still the dominant building material in north-west Europe.


title: Castle

text: Historians have interpreted the widespread presence of castles across Europe in the 11th and 12th centuries as evidence that warfare was common, and usually between local lords. Castles were introduced into England shortly before the Norman Conquest in 1066. Before the 12th century castles were as uncommon in Denmark as they had been in England before the Norman Conquest. The introduction of castles to Denmark was a reaction to attacks from Wendish pirates, and they were usually intended as coastal defences. The motte and bailey remained the dominant form of castle in England, Wales, and Ireland well into the 12th century. At the same time, castle architecture in mainland Europe became more sophisticated.


title: Castle

text: The donjon was at the centre of this change in castle architecture in the 12th century. Central towers proliferated, and typically had a square plan, with walls thick. Their decoration emulated Romanesque architecture, and sometimes incorporated double windows similar to those found in church bell towers. Donjons, which were the residence of the lord of the castle, evolved to become more spacious. The design emphasis of donjons changed to reflect a shift from functional to decorative requirements, imposing a symbol of lordly power upon the landscape. This sometimes led to compromising defence for the sake of display.