Etymology.

"Castrum" appears in Oscan and Umbrian, two other Italic languages, suggesting an origin at least as old as Proto-Italic language.  Julius Pokorny traces a probable derivation from *k̂es-, "schneiden" (“cut”) in *k̂es-tro-m, "Schneidewerkzeug" (“cutting tool”).  These Italic reflexes based on *kastrom include Oscan "castrous" (genitive case) and Umbrian "castruo", "kastruvuf" (accusative case). They have the same meaning, says Pokorny, as Latin "fundus", an estate, or tract of land. This is not any land, but is a prepared or cultivated tract, such as a farm enclosed by a fence or a wooden or stone wall of some kind. Cornelius Nepos uses Latin "castrum" in that sense: when Alcibiades deserts to the Persians, Pharnabazus gives him an estate ("castrum") worth 500 talents in tax revenues. This is a change of meaning from the reflexes in other languages, which still mean some sort of knife, axe, or spear. Pokorny explains it as "’Lager’ als ‘abgeschnittenes Stück Land’", “a lager, as a cut-off piece of land.”  If this is the civilian interpretation, the military version must be “military reservation,” a piece of land cut off from the common land around it and modified for military use. All castra must be defended by works, often no more than a stockade, for which the soldiers carried stakes, and a ditch. The "castra" could be prepared under attack within a hollow square or behind a battle line. Considering that the earliest military shelters were tents made of hide or cloth, and all but the most permanent bases housed the men in tents placed in quadrangles and separated by numbered streets, one "castrum" may well have acquired the connotation of tent.

Linguistic development of the military castra.

The commonest Latin syntagmata (here phrases) for the term "castra" are:  In Latin the term "castrum" is much more frequently used as a proper name for geographical locations: e.g., Castrum Album, Castrum Inui, Castrum Novum, Castrum Truentinum, Castrum Vergium. The plural was also used as a place name, as Castra Cornelia, and from this comes the Welsh place name prefix "caer-" and English suffixes "-caster" and "-chester"; e.g., Winchester, Lancaster.  "Castrorum Filius", "son of the camps," was one of the names used by the emperor Caligula and then also by other emperors.  "Castro", also derived from "Castrum", is a common Spanish family name as well as toponym in Italy, the Balkans and Spain and other Hispanophone countries, either by itself or in various compounds such as the World Heritage Site of Gjirokastër (earlier "Argurokastro").  The terms stratopedon ("army camp") and phrourion ("fortification") were used by Greek language authors to translate "castrum" and "castellum", respectively.

Description.

A "castrum" was designed to house and protect the soldiers, their equipment and supplies when they were not fighting or marching.  The most detailed description that survives about Roman military camps is "De Munitionibus Castrorum", a manuscript of 11 pages that dates most probably from the late 1st to early 2nd century AD.  Regulations required a major unit in the field to retire to a properly constructed camp every day. "... as soon as they have marched into an enemy's land, they do not begin to fight until they have walled their camp about; nor is the fence they raise rashly made, or uneven; nor do they all abide ill it, nor do those that are in it take their places at random; but if it happens that the ground is uneven, it is first levelled: their camp is also four-square by measure, and carpenters are ready, in great numbers, with their tools, to erect their buildings for them." To this end a marching column ported the equipment needed to build and stock the camp in a baggage train of wagons and on the backs of the soldiers.  Camps were the responsibility of engineering units to which specialists of many types belonged, officered by "architecti", "chief engineers", who requisitioned manual labor from the soldiers at large as required. They could throw up a camp under enemy attack in as little as a few hours. Judging from the names, they probably used a repertory of camp plans, selecting the one appropriate to the length of time a legion would spend in it: "tertia castra", "quarta castra", etc. ("a camp of three days", "four days", etc.).  More permanent camps were "castra stativa" ("standing camps"). The least permanent of these were "castra aestiva" or "aestivalia", "summer camps", in which the soldiers were housed "sub pellibus" or "sub tentoriis", "under tents". Summer was the campaign season. For the winter the soldiers retired to "castra hiberna" containing barracks and other buildings of more solid materials, with timber construction gradually being replaced by stone.  The camp allowed the Romans to keep a rested and supplied army in the field. Neither the Celtic nor Germanic armies had this capability: they found it necessary to disperse after only a few days.  The largest castra were "legionary fortresses" built as bases for one or more whole legions.  From the time of Augustus more permanent castra with wooden or stone buildings and walls were introduced as the distant and hard-won boundaries of the expanding empire required permanent garrisons to control local and external threats from war-like tribes. Previously, legions were raised for specific military campaigns and subsequently disbanded, requiring only temporary castra. From then on many castra of various sizes were established many of which became permanent settlements.

Plan of forts.

Sources and origins.

From the most ancient times Roman camps were constructed according to a certain ideal pattern, formally described in two main sources, the "De Munitionibus Castrorum" and the works of Polybius. P. Fl. Vegetius Renatus has a small section on entrenched camps as well. The terminology varies but the basic plan is the same. The hypothesis of an Etruscan origin is a viable alternative.

Layout.

The ideal enforced a linear plan for a camp or fort: a square for camps to contain one legion or smaller unit, a rectangle for two legions, each legion being placed back-to-back with headquarters next to each other. Laying it out was a geometric exercise conducted by experienced officers called "metatores", who used graduated measuring rods called "decempedae" ("10-footers") and "gromatici" who used a groma, a sighting device consisting of a vertical staff with horizontal cross pieces and vertical plumb-lines. Ideally the process started in the centre of the planned camp at the site of the headquarters tent or building (principia). Streets and other features were marked with coloured pennants or rods.  The street plans of various present-day cities still retain traces of a Roman camp, for example Marsala in Sicily, the ancient Lilybaeum, where the name of the main street, the Cassaro, perpetuates the name "castrum".

Wall and ditch.

The Castrum's special structure also defended from attacks.  The base ("munimentum", "fortification") was placed entirely within the "vallum" ("wall"), which could be constructed under the protection of the legion in battle formation if necessary. The "vallum" was quadrangular aligned on the cardinal points of the compass. The construction crews dug a trench ("fossa"), throwing the excavated material inward, to be formed into the rampart ("agger"). On top of this a palisade of stakes ("sudes" or "valli") was erected. The soldiers had to carry these stakes on the march. Over the course of time, the palisade might be replaced by a fine brick or stone wall, and the ditch serve also as a moat. A legion-sized camp always placed towers at intervals along the wall with positions between for the division artillery.

Interval.

Around the inside periphery of the "vallum" was a clear space, the "intervallum", which served to catch enemy missiles, as an access route to the "vallum" and as a storage space for cattle ("capita") and plunder ("praeda"). Legionaries were quartered in a peripheral zone inside the "intervallum", which they could rapidly cross to take up position on the "vallum". Inside of the legionary quarters was a peripheral road, the "Via Sagularis", probably a type of "service road", as the "sagum", a kind of cloak, was the garment of soldiers.

Streets, gates and central plaza.

Every camp included "main street", which ran through the camp in a north-south direction and was very wide. The names of streets in many cities formerly occupied by the Romans suggest that the street was called "cardo" or "cardus maximus". This name applies more to cities than it does to ancient camps.  Typically "main street" was the "via principalis". The central portion was used as a parade ground and headquarters area. The "headquarters" building was called the "praetorium" because it housed the "praetor" or base commander ("first officer"), and his staff. In the camp of a full legion he held the rank of "consul" or "proconsul" but officers of lesser ranks might command.  On one side of the "praetorium" was the "quaestorium", the building of the "quaestor" (supply officer). On the other side was the "forum", a small duplicate of an urban forum, where public business could be conducted. Along the "Via Principalis" were the homes or tents of the several tribunes in front of the barracks of the units they commanded.  The "Via Principalis" went through the "vallum" in the "Porta Principalis Dextra" ("right principal gate") and "Porta Principalis Sinistra" ("left, etc."), which were gates fortified with "turres" ("towers"). Which was on the north and which on the south depends on whether the praetorium faced east or west, which remains unknown.  The central region of the "Via Principalis" with the buildings for the command staff was called the "Principia" (plural of "principium"). It was actually a square, as across this at right angles to the "Via Principalis" was the "Via Praetoria", so called because the "praetorium" interrupted it. The "Via Principalis" and the "Via Praetoria" offered another division of the camp into four quarters. Across the central plaza ("principia") to the east or west was the main gate, the "Porta Praetoria". Marching through it and down "headquarters street" a unit ended up in formation in front of the headquarters. The standards of the legion were located on display there, very much like the flag of modern camps.  On the other side of the praetorium the "Via Praetoria" continued to the wall, where it went through the "Porta Decumana". In theory this was the back gate. Supplies were supposed to come in through it and so it was also called, descriptively, the "Porta Quaestoria". The term Decumana, "of the 10th", came from the arranging of "manipuli" or "turmae" from the first to the 10th, such that the 10th was near the "intervallum" on that side. The "Via Praetoria" on that side might take the name "Via Decumana" or the entire "Via Praetoria" be replaced with "Decumanus Maximus".

Canteen.

In peaceful times the camp set up a marketplace with the natives in the area. They were allowed into the camp as far as the units numbered 5 (half-way to the praetorium). There another street crossed the camp at right angles to the "Via Decumana", called the "Via Quintana", "5th street". If the camp needed more gates, one or two of the "Porta Quintana" were built, presumably named "dextra" and "sinistra". If the gates were not built, the "Porta Decumana" also became the "Porta Quintana". At "5th street" a public market was allowed.

Major buildings.

The "Via Quintana" and the "Via Principalis" divided the camp into three districts: the "Latera Praetorii", the "Praetentura" and the "Retentura". In the "latera" ("sides") were the "Arae" (sacrificial altars), the "Auguratorium" (for auspices), the "Tribunal", where courts martial and arbitrations were conducted (it had a raised platform), the guardhouse, the quarters of various kinds of staff and the storehouses for grain ("horrea") or meat ("carnarea"). Sometimes the "horrea" were located near the barracks and the meat was stored on the hoof. Analysis of sewage from latrines indicates the legionary diet was mainly grain. Also located in the "Latera" was the "Armamentarium", a long shed containing any heavy weapons and artillery not on the wall.  The "Praetentura" ("stretching to the front") contained the "Scamnum Legatorum", the quarters of officers who were below general but higher than company commanders ("Legati"). Near the "Principia" were the "Valetudinarium" (hospital), "Veterinarium" (for horses), "Fabrica" ("workshop", metals and wood), and further to the front the quarters of special forces. These included "Classici" ("marines", as most European camps were on rivers and contained a river naval command), "Equites" ("cavalry"), "Exploratores" ("scouts"), and "Vexillarii" (carriers of vexillae, the official pennants of the legion and its units). Troops who did not fit elsewhere also were there.  The part of the "Retentura" ("stretching to the rear") closest to the "Principia" contained the "Quaestorium". By the late empire it had developed also into a safekeep for plunder and a prison for hostages and high-ranking enemy captives. Near the "Quaestorium" were the quarters of the headquarters guard ("Statores"), who amounted to two centuries (companies). If the "Imperator" was present they served as his bodyguard.

Barracks.

Further from the "Quaestorium" were the tents of the "Nationes" ("natives"), who were auxiliaries of foreign troops, and the legionaries themselves in double rows of tents or barracks ("Strigae"). One "Striga" was as long as required and 18 m wide. In it were two "Hemistrigia" of facing tents centered in its 9 m strip. Arms could be stacked before the tents and baggage carts kept there as well. Space on the other side of the tent was for passage.  In the northern places like Britain, where it got cold in the winter, they would make wood or stone barracks. The Romans would also put a fireplace in the barracks. They had about three bunk beds in it. They had a small room beside it where they put their armour; it was as big as the tents. They would also make these barracks if the fort they had was going to stay there for good.  A tent was 3 by 3.5 metres (0.6 m for the aisle), ten men per tent. Ideally a company took 10 tents, arranged in a line of 10 companies, with the 10th near the "Porta Decumana". Of the c. 9.2 square metres of bunk space each man received 0.9, or about 0.6 by 1.5 m, which was only practical if they slept with heads to the aisle. The single tent with its men was called "contubernium", also used for "squad". A squad during some periods was 8 men or fewer.  The "Centurion", or company commander, had a double-sized tent for his quarters, which served also as official company area. Other than there, the men had to find other places to be. To avoid mutiny, it became extremely important for the officers to keep them busy.  A covered portico might protect the walkway along the tents. If barracks had been constructed, one company was housed in one barracks building, with the arms at one end and the common area at the other. The company area was used for cooking and recreation, such as gaming. The army provisioned the men and had their bread ("panis militaris") baked in outdoor ovens, but the men were responsible for cooking and serving themselves. They could buy meals or supplementary foods at the canteen. The officers were allowed servants.

Sanitation.

For sanitary facilities, a camp had both public and private latrines. A public latrine consisted of a bank of seats situated over a channel of running water. One of the major considerations for selecting the site of a camp was the presence of running water, which the engineers diverted into the sanitary channels. Drinking water came from wells; however, the larger and more permanent bases featured the "aqueduct", a structure running a stream captured from high ground (sometimes miles away) into the camp. The praetorium had its own latrine, and probably the quarters of the high-ranking officers. In or near the "intervallum", where they could easily be accessed, were the latrines of the soldiers. A public bathhouse for the soldiers, also containing a latrine, was located near or on the "Via Principalis".

Territory.

The influence of a base extended far beyond its walls. The total land required for the maintenance of a permanent base was called its "territoria". In it were located all the resources of nature and the terrain required by the base: pastures, woodlots, water sources, stone quarries, mines, exercise fields and attached villages. The central castra might also support various fortified adjuncts to the main base, which were not in themselves self-sustaining (as was the base). In this category were "speculae", "watchtowers", "castella", "small camps", and naval bases.  All the major bases near rivers featured some sort of fortified naval installation, one side of which was formed by the river or lake. The other sides were formed by a polygonal wall and ditch constructed in the usual way, with gates and watchtowers. The main internal features were the boat sheds and the docks. When not in use, the boats were drawn up into the sheds for maintenance and protection. Since the camp was placed to best advantage on a hill or slope near the river, the naval base was usually outside its walls. The "classici" and the "optiones" of the naval installation relied on the camp for its permanent defense. Naval personnel generally enjoyed better quarters and facilities. Many were civilians working for the military.

Modifications in practice.

This ideal was always modified to suit the terrain and the circumstances. Each camp discovered by archaeology has its own specific layout and architectural features, which makes sense from a military point of view.  If, for example, the camp was built on an outcrop, it followed the lines of the outcrop. The terrain for which it was best suited and for which it was probably designed in distant prehistoric times was the rolling plain. The camp was best placed on the summit and along the side of a low hill, with spring water running in rivulets through the camp ("aquatio") and pastureland to provide grazing ("pabulatio") for the animals. In case of attack, arrows, javelins and sling missiles could be fired down at an enemy tiring himself to come up. For defence troops could be formed in an "acies", or "battle-line", outside the gates, where they could be easily resupplied and replenished, as well as being supported by archery from the palisade.  The streets, gates and buildings present depended on the requirements and resources of the camp. The gates might vary from two to six and not be centred on the sides. Not all the streets and buildings might be present.

Quadrangular camps in later times.

Many settlements in Europe originated as Roman military camps and still show traces of their original pattern (e.g. Castres in France, Barcelona in Spain). The pattern was also used by Spanish colonizers in America following strict rules by the Spanish monarchy for founding new cities in the New World.  Many of the towns of England still retain forms of the word "castra" in their names, usually as the suffixes "-caster", "-cester" or "-chester" – Lancaster, Tadcaster, Worcester, Gloucester, Mancetter, Uttoxeter, Colchester, Chester, Manchester and Ribchester for example. Castle has the same derivation, from the diminutive "castellum" or "little fort", but does not usually indicate a former Roman camp. Whitley Castle however is an exception, referring to the Roman fort of Epiacum in Northumberland.

Camp life.

Activities conducted in a castra can be divided into ordinary and "the duty" or "the watch". Ordinary activity was performed during regular working hours. The duty was associated with operating the installation as a military facility. For example, none of the soldiers were required to man the walls all the time, but round-the clock duty always required a portion of the soldiers to be on duty at any time.  Duty time was divided into "vigilia", the eight watches into which the 24-hour day was divided so they stood guard for 3 hours that day. The Romans used signals on brass instruments to mark time. These were mainly the "buccina" or "bucina", the "cornu" and the "tuba". As they did not possess valves for regulating the pitch, the range of these instruments was somewhat limited. Nevertheless, the musicians ("Aenatores", "brassmen") managed to define enough signals for issuing commands. The instrument used to mark the passage of a watch was the "buccina", from which the trumpet derives. It was sounded by a "buccinator".

Ordinary life.

Ordinary camp life began with a "buccina" call at daybreak, the first watch of the day. The soldiers arose at this time and shortly after collected in the company area for breakfast and assembly. The centurions were up before them and off to the "principia" where they and the "equites" were required to assemble. The regimental commanders, the tribunes, were already converging on the "praetorium". There the general staff was busily at work planning the day. At a staff meeting the "Tribunes" received the password and the orders of the day. They brought those back to the "centuriones", who returned to their company areas to instruct the men.  For soldiers, the main item of the agenda was a vigorous training session lasting about a watch long. Recruits received two, one in the morning and one in the afternoon. Planning and supervision of training were under a general staff officer, who might manage training at several camps. According to Vegetius, the men might take a hike or a jog under full pack, or swim a river. Marching drill was always in order.  Each soldier was taught the use of every weapon and also was taught to ride. Seamanship was taught at naval bases. Soldiers were generalists in the military and construction arts. They practiced archery, spear-throwing and above all swordsmanship against posts ("pali") fixed in the ground. Training was taken very seriously and was democratic. Ordinary soldiers would see all the officers training with them including the "praetor", or the Emperor, if he was in camp.  Swordsmanship lessons and use of the shooting range probably took place on the "campus", a "field" outside the "castra", from which English camp derives. Its surface could be lightly paved. Winter curtailed outdoor training. The general might in that case have sheds constructed, which served as field houses for training. There is archaeological evidence in one case of an indoor equestrian ring.  Apart from the training, each soldier had a regular job on the base, of which there were a large variety from the various kinds of clerks to the craftsmen. Soldiers changed jobs frequently. The commander's policy was to have all the soldiers skilled in all the arts and crafts so that they could be as interchangeable as possible. Even then the goal was not entirely achievable. The gap was bridged by the specialists, the "optiones" or "chosen men", of which there were many different kinds. For example, a skilled artisan might be chosen to superintend a workshop. The supply administration was run as a business using money as the medium of exchange. The aureus was the preferred coin of the late republic and early empire; in the late empire the solidus came into use. The larger bases, such as "Moguntiacum", minted their own coins. As does any business, the base quaestorium required careful record keeping, performed mainly by the optiones. A chance cache of tablets from Vindolanda in Britain gives us a glimpse of some supply transactions. They record, among other things, the purchase of consumables and raw supplies, the storage and repair of clothing and other items, and the sale of items, including foodstuffs, to achieve an income. Vindolanda traded vigorously with the surrounding natives.  Another feature of the camp was the military hospital ("valetudinarium", later "hospitium"). Augustus instituted the first permanent medical corps in the Roman army. Its physicians, the "medici ordinarii", had to be qualified physicians. They were allowed medical students, practitioners and whatever orderlies they needed; i.e., the military hospitals were medical schools and places of residency as well.  Officers were allowed to marry and to reside with their families on base. The army did not extend the same privileges to the men, who were not allowed to marry. However, they often kept common law families off base in communities nearby. The communities might be native, as the tribesmen tended to build around a permanent base for purposes of trade, but also the base sponsored villages ("vici") of dependents and businessmen. Dependants were not allowed to follow an army on the march into hostile territory.  Military service was for about 25 years. At the end of that time, the veteran was given a certificate of honorable discharge ("honesta missio"). Some of these have survived engraved on stone. Typically they certify that the veteran, his wife (one per veteran) and children or his sweetheart were now Roman citizens, which is a good indication that troops, which were used chiefly on the frontier, were from peoples elsewhere on the frontier who wished to earn Roman citizenship. However, under Antoninus Pius, citizenship was no longer granted to the children of rank-and-file veterans, the privilege becoming restricted only to officers.  Veterans often went into business in the communities near a base. They became permanent members of the community and would stay on after the troops were withdrawn, as in the notable case of Saint Patrick's family.

Duties.

Conducted in parallel with the ordinary activities was "the duty", the official chores required by the camp under strict military discipline. The "Legate" was ultimately responsible for them as he was for the entire camp, but he delegated the duty to a tribune chosen as officer of the day. The line "Tribunes" were commanders of "Cohortes" and were approximately the equivalent of colonels. The 6 tribunes were divided into units of two, with each unit being responsible for filling the position of officer of the day for two months. The two men of a unit decided among themselves who would take what day. They could alternate days or each take a month. One filled in for the other in case of illness. On his day, the tribune effectively commanded the camp and was even respected as such by the "Legate".  The equivalent concept of the duties performed in modern camps is roughly the detail. The responsibilities ("curae") of the many kinds of detail were distributed to the men by all the methods considered fair and democratic: lot, rotation and negotiation. Certain kinds of "cura" were assigned certain classes or types of troops; for example, wall sentries were chosen only from "Velites". Soldiers could be temporarily or permanently exempted: the "immunes". For example, a Triarius was "immunis" from the "curae" of the Hastati.  The duty year was divided into time slices, typically one or two months, which were apportioned to units, typically maniples or centuries. They were always allowed to negotiate who took the duty and when. The most common kind of "cura" were the posts of the sentinels, called the "excubiae" by day and the "vigilae" at night. Wall posts were "praesidia", gate posts, "custodiae", advance positions before the gates, "stationes".  In addition were special guards and details. One post was typically filled by four men, one sentinel and the others at ease until a situation arose or it was their turn to be sentinel. Some of the details were:

External links.

Below are a number of links to sites reporting or summarizing current research or thinking. Many are reprints of articles made available to the public at no charge. The historical researcher will find their bibliographies of great interest.

In the Roman Republic and the Roman Empire, the Latin word castrum (plural castra) was a building, or plot of land, used as a fortified military camp. In English, the terms "Roman fort", "Roman camp" and "Roman fortress" are commonly used for "castrum". However, scholastic convention tends toward the use of the words "fort", "camp", "marching camp" and "fortress" as a translation of "castrum".

Un camp romain est une installation, durable ou provisoire, construite par les armées romaines pour protéger leur cantonnement. Contrairement à toutes les armées antiques, lorsque les légions de la Rome antique en campagne quittent la zone totalement sûre, elles construisent chaque soir un camp fortifié ("castrum" en latin, pluriel : "castra"). Cette habitude est très ancienne, et remonte peut-être aux réformes de Camille (Marius a plus tard codifié ces habitudes).


History.

The Border Gateway Protocol has been in use on the Internet since 1994. The current version of BGP is version 4 (BGP4), which was published as RFC 4271 in 2006, after progressing through 20 drafts from documents based on RFC 1771 version 4. RFC 4271 corrected errors, clarified ambiguities and updated

Operation.

Ideally, even if impractical, all possible links would connect to one another, like spokes in a bicycle tire. BGP, "the most scalable of all routing protocols," provides a workaround and ways to measure how effectively it is configured.  BGP neighbors, called peers, are established by manual configuration among routers to create a TCP session on port 179. A BGP speaker sends 19-byte keep-alive messages every 60 seconds to maintain the connection. Among routing protocols, BGP is unique in using TCP as its transport protocol.  When BGP runs between two peers in the same autonomous system (AS), it is referred to as "Internal BGP" ("i-BGP" or "Interior Border Gateway Protocol"). When it runs between different autonomous systems, it is called "External BGP" ("eBGP" or "Exterior Border Gateway Protocol"). Routers on the boundary of one AS exchanging information with another AS are called "border" or "edge routers" or simply "eBGP peers" and are typically connected directly, while "i-BGP peers" can be interconnected through other intermediate routers. Other deployment topologies are also possible, such as running eBGP peering inside a VPN tunnel, allowing two remote sites to exchange routing information in a secure and isolated manner. The main difference between iBGP and eBGP peering is in the way routes that were received from one peer are propagated to other peers. For instance, new routes learned from an eBGP peer are typically redistributed to all iBGP peers as well as all other eBGP peers (if "transit" mode is enabled on the router). However, if new routes are learned on an iBGP peering, then they are re-advertised only to all eBGP peers. These route-propagation rules effectively require that all iBGP peers inside an AS are interconnected in a full mesh.  How routes are propagated can be controlled in detail via the "route-maps" mechanism. This mechanism consists of a set of rules. Each rule describes, for routes matching some given criteria, what action should be taken. The action could be to drop the route, or it could be to modify some attributes of the route before inserting it in the routing table.

Extensions negotiation.

During the peering handshake, when OPEN messages are exchanged, BGP speakers can negotiate optional capabilities of the session, including multiprotocol extensions and various recovery modes. If the multiprotocol extensions to BGP are negotiated at the time of creation, the BGP speaker can prefix the Network Layer Reachability Information (NLRI) it advertises with an address family prefix. These families include the IPv4 (default), IPv6, IPv4/IPv6 Virtual Private Networks and multicast BGP. Increasingly, BGP is used as a generalized signaling protocol to carry information about routes that may not be part of the global Internet, such as VPNs.  In order to make decisions in its operations with peers, a BGP peer uses a simple finite state machine (FSM) that consists of six states: Idle; Connect; Active; OpenSent;

Router connectivity and learning routes.

In the simplest arrangement, all routers within a single AS and participating in BGP routing must be configured in a full mesh: each router must be configured as peer to every other router. This causes scaling problems, since the number of required connections grows quadratically with the number of routers involved. To alleviate the problem, BGP implements two options: route reflectors (RFC 4456) and BGP confederations (RFC 5065). The following discussion of basic UPDATE processing assumes a full iBGP mesh.  A given BGP router may accept Network Layer Reachability Information (NLRI) UPDATEs from multiple neighbors and advertise NLRI to the same, or a different set, of neighbors. Conceptually, BGP maintains its own "master" routing table, called the Local Routing Information Base ("Loc-RIB"), separate from the main routing table of the router. For each neighbor, the BGP process maintains a conceptual Adjacent Routing Information Base, Incoming ("Adj-RIB-In") containing the NLRI received from the neighbor, and a conceptual "Adj-RIB-Out" (Outgoing) for NLRI to be sent to the neighbor.  "Conceptual", in the

Communities.

BGP communities are attribute tags that can be applied to incoming or outgoing prefixes to achieve some common goal (RFC 1997). While it is common to say that BGP allows an administrator to set policies on how prefixes are handled by ISPs, this is generally not possible, strictly speaking. For instance, BGP natively has no concept to allow one AS to tell another AS to restrict advertisement of a prefix to only North American peering customers. Instead, an ISP generally publishes a list of well-known or proprietary communities with

Multi-exit discriminators.

MEDs, defined in the main BGP standard, were originally intended to show to another neighbor AS the advertising AS's preference as to which of several

Message header format.

The following is the

Internal scalability.

An autonomous system with internal BGP (iBGP) must have all of its iBGP peers connect to each other in a full mesh (where everyone speaks to everyone directly). This full-mesh configuration requires that each router maintain a session to every other router. In large networks, this number of sessions may degrade performance of routers, due to either a lack of memory, or high CPU process requirements.

Route reflectors.

Route reflectors reduce the number of connections required in an AS. A single router (or two for redundancy) can be made a route reflector: other routers in the AS need only be configured as peers to them. A route reflector offers an alternative to the logical full-mesh requirement of internal border gateway protocol (IBGP). A RR acts as a for IBGP sessions. The purpose of the RR is concentration. Multiple BGP routers can peer with a central point, the RR – acting as a route reflector server – rather than peer with every other router in a full mesh. All the other IBGP routers become route reflector clients.  This approach, similar

Rules.

RR servers propagate routes inside

Cluster.

RR and its clients form a "Cluster". The "Cluster-ID" is then attached to every route advertised by RR to its client or nonclient peers. Cluster-ID is a cumulative, non-transitive BGP attribute and every RR MUST prepend the local CLUSTER_ID to the CLUSTER_LIST in order to avoid routing loops. Route reflectors and confederations both reduce the number of iBGP peers to each router and thus reduce processing overhead. Route reflectors are a pure performance-enhancing technique, while confederations also can be used to implement more fine-grained policy.

BGP confederation.

Confederations are sets of autonomous systems. In common practice, only one of the confederation AS numbers is seen by the Internet as a whole. Confederations are used in very large networks where a large AS can be configured to encompass smaller more manageable internal ASs.  The confederated AS is composed of multiple ASs. Each confederated AS alone has iBGP fully meshed and has connections to other ASs inside the confederation. Even though these ASs have eBGP peers to ASs within the confederation, the ASs exchange routing as if they used iBGP. In this

Stability.

The routing tables managed by a BGP implementation are adjusted continually to reflect actual changes in the network, such as links breaking and being restored or routers going down and coming back up. In the network as a whole it is normal for these changes to happen almost continuously, but for any particular router or link, changes are supposed to be relatively infrequent. If a router is misconfigured or mismanaged then it may get into a rapid cycle between down and up states. This pattern of repeated withdrawal and re-announcement known as route flapping can cause excessive activity in all the other routers that know about the broken link, as the same route is continually injected and withdrawn from the routing tables. The BGP design is such that delivery of traffic may not function while routes are being updated. On the Internet, a BGP routing change may cause outages for several minutes.  A feature known as "route flap damping" (RFC 2439) is built into many BGP implementations in an attempt to mitigate the effects of route flapping. Without damping, the excessive activity can cause a heavy processing load on routers, which may in turn delay updates on other routes, and so affect overall routing stability. With damping, a route's flapping is exponentially decayed. At the first instance when a route becomes unavailable and quickly reappears, damping does

Routing table growth.

One of the largest problems faced by BGP, and indeed the Internet infrastructure as a whole, is the growth of the Internet routing table. If the global routing table grows to the point where some older, less capable routers cannot cope with the memory requirements or the CPU load of maintaining the table, these routers will cease to be effective gateways between the parts of the Internet they connect. In addition, and perhaps even more importantly, larger routing tables take longer to stabilize (see above) after a major connectivity change, leaving network service unreliable, or even unavailable, in the interim.  Until late 2001, the global routing table was growing exponentially, threatening an eventual widespread breakdown of connectivity. In an attempt to prevent this, ISPs cooperated in keeping the global routing table as small as possible, by using Classless Inter-Domain Routing (CIDR) and route aggregation. While this slowed the growth of the routing table to a linear process for several years, with the expanded demand for multihoming by end user networks the growth was once again superlinear by the middle of 2004.

512k day.

A Y2K-like overflow triggered in 2014 for those models that were not appropriately updated.  While a full IPv4 BGP table (512k day) is in excess of 512,000 prefixes, many older routers have a limit of 512k (512,000–524,288) routing table entries. On August 12, 2014, outages resulting from full tables hit eBay, LastPass and Microsoft Azure among others. A number of Cisco routers commonly in use have TCAM, a form of high-speed content-addressable memory, for storing BGP advertised routes. On impacted routers, the TCAM is default allocated to 512k entries for IPv4 routes, and 512k entries for

AS numbers depletion and 32 bits ASN.

The RFC 1771 ("A Border Gateway Protocol 4 (BGP-4)") planned the coding of AS numbers on 16 bits, for 64510 possible public AS, since ASN 64512 to 65534 were reserved for private use (0 and 65535 being forbidden). In 2011, only 15000 AS numbers were still available, and projections were envisioning a complete depletion of available AS numbers

Load balancing.

Another factor causing this growth of the routing table is the need for load balancing of multi-homed networks. It is not a trivial task to balance the inbound traffic to a multi-homed network across its multiple inbound paths, due to limitation of the BGP route selection process. For a multi-homed network, if it announces the same network blocks across all of its BGP peers, the result may be that one or several of its inbound links become congested while the other links remain under-utilized, because external networks all picked

Security.

By design, routers running BGP accept advertised routes from other BGP routers by default. This allows for automatic and decentralized routing of traffic across the Internet, but it also leaves the Internet potentially vulnerable to accidental or malicious disruption, known as

Extensions.

An extension to BGP is the use of multipathing this typically requires identical MED, weight, origin, and AS-path although some implementations provide the ability to relax the AS-path checking to only expect an equal path length rather than the actual AS numbers in the path being expected to match too. This can then be extended further with features like Cisco's dmzlink-bw which enables a ratio of traffic sharing based on bandwidth values configured on individual links.  Multiprotocol Extensions for BGP (MBGP), sometimes referred to as Multiprotocol BGP or Multicast BGP and defined in IETF <nowiki>RFC 4760</nowiki>, is an extension to (BGP) that allows

Uses.

BGP4 is standard for Internet routing and required of most Internet service providers (ISPs) to establish routing between one another. Very large private IP networks use BGP internally. An example is the

Implementations.

Routers, especially small ones intended for Small Office/Home Office (SOHO) use, may not include BGP software. Some SOHO routers simply are not capable of running BGP / using BGP routing tables of any size. Other commercial routers may need a specific software executable image that contains BGP, or a license that enables it. Open source packages that run BGP include GNU Zebra, Quagga, OpenBGPD, BIRD, XORP, and Vyatta. Devices marketed as Layer 3 switches are less likely to support BGP than devices marketed as routers, but high-end Layer 3 Switches usually can run BGP.  Products marketed as switches may or may not have a size limitation on BGP tables, such as 20,000 routes, far smaller than a full Internet table plus internal routes. These devices, however, may be perfectly reasonable and useful when used for BGP routing of some smaller part of the network, such as a confederation-AS representing one of several smaller enterprises that are linked, by a BGP backbone of backbones, or a small enterprise that announces routes to an ISP but only accepts a default route and perhaps a small number of aggregated routes.  A BGP router used only for a network with a single point of entry to the Internet may have a much smaller routing table size (and hence RAM and CPU requirement) than a multihomed network. Even simple multihoming can have modest routing table size. See RFC 4098 for vendor-independent performance parameters for single BGP router convergence in the control plane. The actual amount of memory required in a BGP router depends on the amount of BGP information exchanged with other BGP speakers and the way in which the particular router stores BGP information. The router may have to keep more than one copy of a route, so it can manage different policies for route advertising and acceptance to a specific neighboring AS. The term view is often used for these different policy relationships on a running router.  If one router implementation takes more memory per route than another implementation, this may be a legitimate design choice, trading processing speed against memory. A full IPv4 BGP table is in excess of 590,000 prefixes. Large ISPs may add another 50% for internal and customer routes. Again depending on implementation, separate tables may be kept for each view of a different peer AS.  Notable free and open source implementations of BGP include:  Systems for testing BGP conformance, load or stress performance come from vendors such as:

Border Gateway Protocol (BGP) is a standardized exterior gateway protocol designed to exchange routing and reachability information among autonomous systems (AS) on the Internet. BGP is classified as a path-vector routing protocol, and it makes routing decisions based on paths, network policies, or rule-sets configured by a network administrator.

Border Gateway Protocol (BGP) est un protocole d'échange de route externe (un EGP), utilisé notamment sur le réseau Internet. Son objectif principal est d'échanger des informations de routage et d'accessibilité de réseaux (appelés "préfixes") entre "Autonomous Systems" (AS). Comme il circule sur TCP, il est considéré comme appartenant à la couche application du modèle OSI.


Notation.

Various notations are used in the literature to denote that two elements and of a set are equivalent with respect to an equivalence relation ; the most common are "" and "", which are used when is implicit, and variations of "", "", or "" to specify explicitly. Non-equivalence may be written "" or "formula_1".

Definition.

A given binary relation ~ on a set "X" is said to be an equivalence relation if and only if it is reflexive, symmetric and transitive. That is, for all "a", "b" and "c" in "X":  "X" together with the relation ~ is called a setoid. The equivalence class of formula_2 under ~, denoted formula_3, is defined as formula_4.

Examples.

Simple example.

Let the set formula_5 have the equivalence relation formula_6. The following sets are equivalence classes of this relation:  The set of all equivalence classes for this relation is formula_8. This set is a partition of the set formula_5.

Equivalence relations.

The following are all equivalence relations:

Well-definedness under an equivalence relation.

If ~ is an equivalence relation on "X", and "P"("x") is a property of elements of "X", such that whenever "x" ~ "y", "P"("x") is true if "P"("y") is true, then the property "P" is said to be well-defined or a "class invariant" under the relation ~.  A frequent particular case occurs when "f" is a function from "X" to another set "Y"; if "x" ~ "x" implies "f"("x") = "f"("x") then "f" is said to be a "morphism" for ~, a "class invariant under" ~, or simply "invariant under" ~. This occurs, e.g. in the character theory of finite groups. The latter case with the function "f" can be expressed by a commutative triangle. See also invariant. Some authors use "compatible with ~" or just "respects ~" instead of "invariant under ~".  More generally, a function may map equivalent arguments (under an equivalence relation ~) to equivalent values (under an equivalence relation ~). Such a function is known as a morphism from ~ to ~.

Equivalence class, quotient set, partition.

Let formula_12. Some definitions:

Equivalence class.

A subset "Y" of "X" such that "a" ~ "b" holds for all "a" and "b" in "Y", and never for "a" in "Y" and "b" outside "Y", is called an equivalence class of "X" by ~. Let formula_13 denote the equivalence class to which "a" belongs. All elements of "X" equivalent to each other are also elements of the same equivalence class.

Quotient set.

The set of all equivalence classes of "X" by ~, denoted formula_14, is the quotient set of "X" by ~. If "X" is a topological space, there is a natural way of transforming "X"/~ into a topological space; see quotient space for the details.

Projection.

The projection of ~ is the function formula_15 defined by formula_16 which maps elements of "X" into their respective equivalence classes by ~.

Equivalence kernel.

The equivalence kernel of a function "f" is the equivalence relation ~ defined by formula_17. The equivalence kernel of an injection is the identity relation.

Partition.

A partition of "X" is a set "P" of nonempty subsets of "X", such that every element of "X" is an element of a single element of "P". Each element of "P" is a "cell" of the partition. Moreover, the elements of "P" are pairwise disjoint and their union is "X".

Counting partitions.

Let "X" be a finite set with "n" elements. Since every equivalence relation over "X" corresponds to a partition of "X", and vice versa, the number of equivalence relations on "X" equals the number of distinct partitions of "X", which is the "n"th Bell number "B":

Fundamental theorem of equivalence relations.

A key result links equivalence relations and partitions: In both cases, the cells of the partition of "X" are the equivalence classes of "X" by ~. Since each element of "X" belongs to a unique cell of any partition of "X", and since each cell of the partition is identical to an equivalence class of "X" by ~, each element of "X" belongs to a unique equivalence class of "X" by ~. Thus there is a natural bijection between the set of all equivalence relations on "X" and the set of all partitions of "X".

Comparing equivalence relations.

If ~ and ≈ are two equivalence relations on the same set "S", and "a"~"b" implies "a"≈"b" for all "a","b" ∈ "S", then ≈ is said to be a coarser relation than ~, and ~ is a finer relation than ≈. Equivalently,  The equality equivalence relation is the finest equivalence relation on any set, while the universal relation, which relates all pairs of elements, is the coarsest.  The relation "~ is finer than ≈" on the collection of all equivalence relations on a fixed set is itself a partial order relation, which makes the collection a geometric lattice.

Generating equivalence relations.

Given any binary relation formula_19 on formula_20, the equivalence relation generated by formula_21 is the intersection of the equivalence relations on formula_22 that contain formula_23. (Since formula_24 is an equivalence relation, the intersection is nontrivial.)

Algebraic structure.

Much of mathematics is grounded in the study of equivalences, and order relations. Lattice theory captures the mathematical structure of order relations. Even though equivalence relations are as ubiquitous in mathematics as order relations, the algebraic structure of equivalences is not as well known as that of orders. The former structure draws primarily on group theory and, to a lesser extent, on the theory of lattices, categories, and groupoids.

Group theory.

Just as order relations are grounded in ordered sets, sets closed under pairwise supremum and infimum, equivalence relations are grounded in partitioned sets, which are sets closed under bijections that preserve partition structure. Since all such bijections map an equivalence class onto itself, such bijections are also known as permutations. Hence permutation groups (also known as transformation groups) and the related notion of orbit shed light on the mathematical structure of equivalence relations.  Let '~' denote an equivalence relation over some nonempty set "A", called the universe or underlying set. Let "G" denote the set of bijective functions over "A" that preserve the partition structure of "A": ∀"x" ∈ "A" ∀"g" ∈ "G" ("g"("x") ∈ ["x"]). Then the following three connected theorems hold:  In sum, given an equivalence relation ~ over "A", there exists a transformation group "G" over "A" whose orbits are the equivalence classes of "A" under ~.  This transformation group characterisation of equivalence relations differs fundamentally from the way lattices characterize order relations. The arguments of the lattice theory operations meet and join are elements of some universe "A". Meanwhile, the arguments of the transformation group operations composition and inverse are elements of a set of bijections, "A" → "A".  Moving to groups in general, let "H" be a subgroup of some group "G". Let ~ be an equivalence relation on "G", such that "a" ~ "b" ↔ ("ab" ∈ "H"). The equivalence classes of ~—also called the orbits of the action of "H" on "G"—are the right cosets of "H" in "G". Interchanging "a" and "b" yields the left cosets.  Related thinking can be found in Rosen (2008: chpt. 10).

Categories and groupoids.

Let "G" be a set and let "~" denote an equivalence relation over "G". Then we can form a groupoid representing this equivalence relation as follows. The objects are the elements of "G", and for any two elements "x" and "y" of "G", there exists a unique morphism from "x" to "y" if and only if "x"~"y".  The advantages of regarding an equivalence relation as a special case of a groupoid include:

Lattices.

The equivalence relations on any set "X", when ordered by set inclusion, form a complete lattice, called Con "X" by convention. The canonical map ker: "X"^"X" → Con "X", relates the monoid "X"^"X" of all functions on "X" and Con "X". ker is surjective but not injective. Less formally, the equivalence relation ker on "X", takes each function "f": "X"→"X" to its kernel ker "f". Likewise, ker(ker) is an equivalence relation on "X"^"X".

Equivalence relations and mathematical logic.

Equivalence relations are a ready source of examples or counterexamples. For example, an equivalence relation with exactly two infinite equivalence classes is an easy example of a theory which is ω-categorical, but not categorical for any larger cardinal number.  An implication of model theory is that the properties defining a relation can be proved independent of each other (and hence necessary parts of the definition) if and only if, for each property, examples can be found of relations not satisfying the given property while satisfying all the other properties. Hence the three defining properties of equivalence relations can be proved mutually independent by the following three examples:  Properties definable in first-order logic that an equivalence relation may or may not possess include:

Euclidean relations.

Euclid's "The Elements" includes the following "Common Notion 1":  Nowadays, the property described by Common Notion 1 is called Euclidean (replacing "equal" by "are in relation with"). By "relation" is meant a binary relation, in which "aRb" is generally distinct from "bRa". A Euclidean relation thus comes in two forms:  The following theorem connects Euclidean relations and equivalence relations:  with an analogous proof for a right-Euclidean relation. Hence an equivalence relation is a relation that is "Euclidean" and "reflexive". "The Elements" mentions neither symmetry nor reflexivity, and Euclid probably would have deemed the reflexivity of equality too obvious to warrant explicit mention.

In mathematics, an equivalence relation is a binary relation that is reflexive, symmetric and transitive. The relation "is equal to" is the canonical example of an equivalence relation, where for any objects,, and :

La notion ensembliste de relation d'équivalence est omniprésente en mathématiques. Elle permet, dans un ensemble, de mettre en relation des éléments qui sont similaires par une certaine propriété.


History.

Within the European Union, local and regional authorities have lobbied for an increased say in EU affairs. This resulted in the creation of the European Committee of the Regions by the Maastricht Treaty, and the provision for Member States to be represented in the Council of the EU by ministers from their regional governments.

Principles.

There are three main principles at the heart of the Committee's work:

Scope.

The Treaties oblige the European Commission and the Council of the European Union to consult the Committee of the Regions whenever new proposals are made in areas that have repercussions at regional or local level. Outside these areas, the Commission, Council and European Parliament have the option to consult the CoR on issues if they see important regional or local implications to a proposal. The CoR can also draw up an opinion on its own initiative, which enables it to put issues on the EU agenda.  The CoR has gained the right (privileged status) to approach the European Court of Justice now that the Treaty of Lisbon has entered into force following ratification by all EU Member States (Article 8, Protocol (No. 2) on the Application of the Principles of Subsidiarity and Proportionality).

Composition.

The CoR has 329 full members and the same number of alternate members. The number from each EU country reflects the size of its population, but ranges from a representation of an average of 88087 citizens of Malta per seat to 3.45 million citizens per German seat. Its members are locally and regionally elected representatives including mayors, regional presidents and councillors. The numbers per country are as follows:

Internal structure.

President.

Elected for a two-and-a-half-year term at the plenary assembly, the President guides the Committee's work, chairs plenary sessions and is the CoR's official representative. Karl-Heinz Lambertz (Belgium / Party of European Socialists, PES), President of the Parliament of the German-speaking Community of Belgium was elected President of the European Committee of the Regions on 12 July 2017. On 12 February 2020, he was replaced by Apostolos Tzitzikostas (Greece / European People's Party, EPP).

First Vice-President.

The First Vice-President is also elected by the plenary assembly for two-and-a-half years and represents the President in the latter's absence. Markku Markkula (Finland / European People's Party, EPP), member of the Espoo City Council was elected First Vice-President of the European Committee of the Regions on 12 July 2017. On 12 February 2020, he was replaced by Vasco Alves Cordeiro (Portugal / Party of European Socialists, PES).

Bureau.

The Bureau is the executive body of the CoR. It comprises 61 members: the President, the First Vice-President, the Presidents of the 6 political groups, one vice-president per Member State (27), and 26 other members from the national delegations, enabling it to reflect national and political balances. The Bureau generally meets seven or eight times a year to draw up the CoR policy programme and instructs the administration on the implementation of its decisions.

Plenary assembly.

The members of the CoR meet in plenary session in Brussels six times a year, to discuss and adopt opinions, reports and resolutions.

CoR commissions.

The CoR structures its work by means of six thematic commissions, which specialise in topical areas:  They prepare draft opinions and hold conferences and seminars focused on their areas of competence. Each commission has approximately 100 members (each member can be part of two commissions) and is supported by a secretariat within the administration. A special Commission for Financial and Administrative Affairs (CFAA) is also established to assist the CoR Bureau.

Political groups.

The CoR has six political groups: the Progressive Alliance of Socialists and Democrats (PES), the European People’s Party (EPP), Renew Europe (RE), the European Alliance (EA), the European Conservatives and Reformists (ECR) and The Greens (GRE). The members of each political group meet before major meetings to adopt common positions.

Conference of Presidents.

The CoR President, First Vice-President, Presidents of the political groups and the Secretary General gather within a Conference of Presidents before each plenary session and other important meetings, with the aim of reaching a political consensus on strategic questions.

National delegations.

The CoR also comprises 27 national delegations. Members meet in their national delegations before plenary sessions and other events to discuss common positions.

Secretary-General.

The Secretary-General is appointed for five years by the Bureau. As head of the CoR administration, the Secretary-General must not hold a political mandate. He is responsible for implementing President's and Bureau decisions and the smooth running of the CoR administration. Petr Blížkovský is the CoRs' Secretary-General since 16 December 2019.

Secretariat-General.

The Secretariat-General consists of five directorates: Members and Plenaries; Legislative Work 1; Legislative Work 2; Communication; Human Resources and Finance. The Logistics and Translations Directorates are jointly managed with the European Economic and Social Committee. The total number of CoR staff in 2015 was 527.

Budget.

Compared to the substantially increased role of the CoR in the global EU framework, as indicated by the Lisbon Treaty, the CoR remains a lean and very efficient organisation, which makes it the third smallest EU institution in terms of budgetary needs. The CoR's 2013 budget (€36.5M) represents only 0.06% of the total EU budget. Its 2014 budget (€90.2M) breakdown according to purpose of expenditure is as follows: 39.7% - Consultative Works (€35.8M); 30.3% - Translation, Interpretation and Print (€27.2M); 30% - Administration and Functioning (€27M). The CoR's 2015 budget was €89.2M. Although all CoR expenditure formally falls under Heading 5 (Administrative expenditure) of the EU Budget, as is the case for the European Parliament budget, a substantial part of its budget relates to non-administrative expenditure. Most obvious examples are all CoR expenses related to its Members and their political activities.

Work.

Opinions.

The European Commission, Council of Ministers and European Parliament consult the CoR when drawing up legislative texts (directives, regulations, etc.) on areas affecting local and regional authorities. The draft texts are forwarded to the relevant CoR commission. A rapporteur is then appointed to draw up the Committee's opinion. This draft opinion must be adopted by the CoR commission before being discussed at the plenary session. Once it has been approved in plenary, the official opinion is sent to all the European institutions and published in the Official Journal of the European Union.

Resolutions.

Resolutions enable the Committee to express its view on important and topical issues. The CoR's political groups or 32 CoR members can draw up resolutions.

Studies and other publications.

The CoR produces studies on various aspects of the local and regional dimension of the EU (education, transport, social issues, enlargement, etc.). They are drawn up with the help of outside experts. The CoR also produces publications for both the general public and for regional and local players, aimed at explaining its activities and outlining current political developments.

Events.

As a meeting place for regions and cities, the CoR organises conferences, seminars and exhibitions in cooperation with local and regional partners and other EU institutions. Once a year, during the European Week of Regions and Cities, the CoR welcomes to its headquarters thousands of participants who take part in lively discussions or seek partners to collaborate on joint projects.  July 2013 — EU enlargement

Key dates.

Early 2020 — Brexit and Greens.

Following Brexit (31 January), the number of CoR Members decreased to 329 due to the removal of the 24 members from the United Kingdom. As of February, a new Political Group was represented in the CoR, The Greens.

The European Committee of the Regions (CoR) is the European Union's (EU) assembly of local and regional representatives that provides sub-national authorities (i.e. regions, counties, provinces, municipalities and cities) with a direct voice within the EU's institutional framework.

Le Comité européen des régions (CdR) est l'assemblée des représentants locaux et régionaux de l'Union européenne qui permet aux pouvoirs infranationaux (régions, comtés, provinces, départements, communes, villes, etc.) de faire entendre directement leur voix au sein du système institutionnel de l'UE.


History.

Following pioneering research into the Big Bang and the formation of helium in stars, an unknown process responsible for producing heavier elements found on Earth from hydrogen and helium was suspected to exist. One early attempt at explanation came from Chandrasekhar and Louis R. Henrich who postulated that elements were produced at temperatures between 6×10 and 8×10 K. Their theory accounted for elements up to chlorine, though there was no explanation for elements of atomic weight heavier than 40 amu at non-negligible abundances. This became the foundation of a study by Fred Hoyle, who hypothesized that conditions in the core of collapsing stars would enable nucleosynthesis of the remainder of the elements via rapid capture of densely packed free neutrons. However, there remained unanswered questions about equilibrium in stars that was required to balance beta-decays and precisely account for abundances of elements that would be formed in such conditions.  The need for a physical setting providing rapid neutron capture, which was known to almost certainly have a role in element formation, was also seen in a table of abundances of isotopes of heavy elements by Hans Suess and Harold Urey in 1956. Their abundance table revealed larger than average abundances of natural isotopes containing magic numbers of neutrons as well as abundance peaks about 10 amu lighter than stable nuclei containing magic numbers of neutrons which were also in abundance, suggesting that radioactive neutron-rich nuclei having the magic neutron numbers but roughly ten fewer protons were formed. These observations also implied that rapid neutron capture occurred faster than beta decay, and the resulting abundance peaks were caused by so-called "waiting points" at magic numbers. This process, rapid neutron capture by neutron-rich isotopes, became known as the "r"-process, whereas the "s"-process was named for its characteristic slow neutron capture. A table apportioning the heavy isotopes phenomenologically between "s"-process and "r"-process isotopes was published in 1957 in the BFH review paper, which named the "r"-process and outlined the physics that guides it. Alastair G. W. Cameron also published a smaller study about the "r"-process in the same year.  The stationary "r"-process as described by the BFH paper was first demonstrated in a time-dependent calculation at Caltech by Phillip A. Seeger, William A. Fowler and Donald D. Clayton, who found that no single temporal snapshot matched the solar "r"-process abundances, but, that when superposed, did achieve a successful characterization of the "r"-process abundance distribution. Shorter-time distributions emphasize abundances at atomic weights less than, whereas longer-time distributions emphasized those at atomic weights greater than. Subsequent treatments of the "r"-process reinforced those temporal features. Seeger "et al." were also able to construct more quantitative apportionment between "s"-process and "r"-process of the abundance table of heavy isotopes, thereby establishing a more reliable abundance curve for the "r"-process isotopes than BFH had been able to define. Today, the "r"-process abundances are determined using their technique of subtracting the more reliable "s"-process isotopic abundances from the total isotopic abundances and attributing the remainder to "r"-process nucleosynthesis. That "r"-process abundance curve (vs. atomic weight) has provided for many decades the target for theoretical computations of abundances synthesized by the physical "r"-process.  The creation of free neutrons by electron capture during the rapid collapse to high density of a supernova core along with quick assembly of some neutron-rich seed nuclei makes the "r"-process a "primary nucleosynthesis process", meaning a process that can occur even in a star initially of pure H and He, in contrast to the BFH designation as a "secondary process" building on preexisting iron. Primary stellar nucleosynthesis begins earlier in the galaxy than does secondary nucleosynthesis. Alternatively the high density of neutrons within neutron stars would be available for rapid assembly into "r"-process nuclei if a collision were to eject portions of a neutron star, which then rapidly expands freed from confinement. That sequence could also begin earlier in galactic time than would "s"-process nucleosynthesis; so each scenario fits the earlier growth of "r"-process abundances in the galaxy. Each of these scenarios is the subject of active theoretical research. Observational evidence of the early "r"-process enrichment of interstellar gas and of subsequent newly formed of stars, as applied to the abundance evolution of the galaxy of stars, was first laid out by James W. Truran in 1981. He and subsequent astronomers showed that the pattern of heavy-element abundances in the earliest metal-poor stars matched that of the shape of the solar "r"-process curve, as if the "s"-process component were missing. This was consistent with the hypothesis that the "s"-process had not yet begun to enrich interstellar gas when these young stars missing the "s"-process abundances were born from that gas, for it requires about 100 million years of galactic history for the "s"-process to get started whereas the "r"-process can begin after two million years. These "s"-process–poor, "r"-process–rich stellar compositions must have been born earlier than any "s"-process, showing that the "r"-process emerges from quickly evolving massive stars that become supernovae and leave neutron-star remnants that can merge with another neutron star. The primary nature of the early "r"-process thereby derives from observed abundance spectra in old stars that had been born early, when the galactic metallicity was still small, but that nonetheless contain their complement of "r"-process nuclei.  Either interpretation, though generally supported by supernova experts, has yet to achieve a totally satisfactory calculation of "r"-process abundances because the overall problem is numerically formidable, but existing results are supportive. In 2017, new data about the "r"-process was discovered when the LIGO and Virgo gravitational-wave observatories discovered a merger of two neutron stars ejecting "r"-process matter. See Astrophysical sites below.  Noteworthy is that the "r"-process is responsible for our natural cohort of radioactive elements, such as uranium and thorium, as well as the most neutron-rich isotopes of each heavy element.

Nuclear physics.

There are three candidate sites for "r"-process nucleosynthesis where the required conditions are thought to exist: low-mass supernovae, Type II supernovae, and neutron star mergers.  Immediately after the severe compression of electrons in a Type II supernova, beta-minus decay is blocked. This is because the high electron density fills all available free electron states up to a Fermi energy which is greater than the energy of nuclear beta decay. However, nuclear capture of those free electrons still occurs, and causes increasing neutronization of matter. This results in an extremely high density of free neutrons which cannot decay, on the order of 10 neutrons per cm), and high temperatures. As this re-expands and cools, neutron capture by still-existing heavy nuclei occurs much faster than beta-minus decay. As a consequence, the "r"-process runs up along the neutron drip line and highly-unstable neutron-rich nuclei are created.  Three processes which affect the climbing of the neutron drip line are a notable decrease in the neutron-capture cross section in nuclei with closed neutron shells, the inhibiting process of photodisintegration, and the degree of nuclear stability in the heavy-isotope region. Neutron captures in "r"-process nucleosynthesis leads to the formation of neutron-rich, weakly bound nuclei with neutron separation energies as low as 2 MeV. At this stage, closed neutron shells at "N" = 50, 82, and 126 are reached, and neutron capture is temporarily paused. These so-called waiting points are characterized by increased binding energy relative to heavier isotopes, leading to low neutron capture cross sections and a buildup of semi-magic nuclei that are more stable toward beta decay. In addition, nuclei beyond the shell closures are susceptible to quicker beta decay owing to their proximity to the drip line; for these nuclei, beta decay occurs before further neutron capture. Waiting point nuclei are then allowed to beta decay toward stability before further neutron capture can occur, resulting in a slowdown or "freeze-out" of the reaction.  Decreasing nuclear stability terminates the "r"-process when its heaviest nuclei become unstable to spontaneous fission, when the total number of nucleons approaches 270. The fission barrier may be low enough before 270 such that neutron capture might induce fission instead of continuing up the neutron drip line. After the neutron flux decreases, these highly unstable radioactive nuclei undergo a rapid succession of beta decays until they reach more stable, neutron-rich nuclei. While the "s"-process creates an abundance of stable nuclei having closed neutron shells, the "r"-process, in neutron-rich predecessor nuclei, creates an abundance of radioactive nuclei about 10 amu below the "s"-process peaks after their decay back to stability.  The "r"-process also occurs in thermonuclear weapons, and was responsible for the initial discovery of neutron-rich almost stable isotopes of actinides like plutonium-244 and the new elements einsteinium and fermium (atomic numbers 99 and 100) in the 1950s. It has been suggested that multiple nuclear explosions would make it possible to reach the island of stability, as the affected nuclides (starting with uranium-238 as seed nuclei) would not have time to beta decay all the way to the quickly spontaneously fissioning nuclides at the line of beta stability before absorbing more neutrons in the next explosion, thus providing a chance to reach neutron-rich superheavy nuclides like copernicium-291 and -293 which should have half-lives of centuries or millennia.

Astrophysical sites.

The most probable candidate site for the "r"-process has long been suggested to be core-collapse supernovae (spectral types "Ib", "Ic" and "II"), which may provide the necessary physical conditions for the "r"-process. However, the very low abundance of "r"-process nuclei in the interstellar gas limits the amount each can have ejected. It requires either that only a small fraction of supernovae eject "r"-process nuclei to the interstellar medium, or that each supernova ejects only a very small amount of "r"-process material. The ejected material must be relatively neutron-rich, a condition which has been difficult to achieve in models, so that astrophysicists remain uneasy about their adequacy for successful "r"-process yields.  In 2017, entirely new astronomical data about the "r"-process was discovered in data about the merger of two neutron stars. Using the gravitational wave data captured in GW170817 to identify the location of the merger, several teams observed and studied optical data of the merger, finding spectroscopic evidence of "r"-process material thrown off by the merging neutron stars. The bulk of this material seems to consist of two types: hot blue masses of highly radioactive "r"-process matter of lower-mass-range heavy nuclei ( such as strontium) and cooler red masses of higher mass-number "r"-process nuclei () rich in actinides (such as uranium, thorium, and californium). When released from the huge internal pressure of the neutron star, these ejecta expand and form seed heavy nuclei that rapidly capture free neutrons, and radiate detected optical light for about a week. Such duration of luminosity would not be possible without heating by internal radioactive decay, which is provided by "r"-process nuclei near their waiting points. Two distinct mass regions ( and ) for the "r"-process yields have been known since the first time dependent calculations of the "r"-process. Because of these spectroscopic features it has been argued that such nucleosynthesis in the Milky Way has been primarily ejecta from neutron-star mergers rather than from supernovae.  These results offer a new possibility for clarifying six decades of uncertainty over the site of origin of "r"-process nuclei. Confirming relevance to the "r"-process is that it is radiogenic power from radioactive decay of "r"-process nuclei that maintains the visibility of these spun off "r"-process fragments. Otherwise they would dim quickly. Such alternative sites were first seriously proposed in 1974 as decompressing neutron star matter. It was proposed such matter is ejected from neutron stars merging with black holes in compact binaries. In 1989 (and 1999) this scenario was extended to binary neutron star mergers (a binary star system of two neutron stars that collide). After preliminary identification of these sites, the scenario was confirmed in GW170817. Current astrophysical models suggest that a single neutron star merger event may have generated between 3 and 13 Earth masses of gold.

In nuclear astrophysics, the rapid neutron-capture process, also known as the "r"-process, is a set of nuclear reactions that is responsible for the creation of approximately half of the atomic nuclei heavier than iron; the "heavy elements", with the other half produced by the p-process and "s"-process. The "r"-process usually synthesizes the most neutron-rich stable isotopes of each heavy element. The "r"-process can typically synthesize the heaviest four isotopes of every heavy element, and the two heaviest isotopes, which are referred to as "r-only nuclei", can only be created via the "r"-process. Abundance peaks for the "r"-process occur near mass numbers (elements Se, Br, and Kr), (elements Te, I, and Xe) and (elements Os, Ir, and Pt).

Le ("r" pour "rapide") est un processus de nucléosynthèse qui consiste en la capture de neutrons par des noyaux atomiques à haute température et à grande densité de neutrons, permettant la fusion nucléaire d'éléments lourds à partir d'éléments plus légers.


Early life.

Naomi Sapir was born to Rivka and Meir Sapir (Sapirov) in Kvutzat Kinneret, an Israeli kibbutz her parents had helped found, on the shores of the Sea of Galilee. In the 1950s she served in the Israeli Defense Force's Nahal entertainment troupe, and studied music at the Rubin Academy in Jerusalem, and in Tel Aviv with Paul Ben-Haim, Abel Ehrlich, Ilona Vincze-Kraus and Josef Tal.

Songwriting career.

Shemer did her own songwriting and composing, set famous poems to music, such as those of the Israeli poet, Rachel, and the American Walt Whitman. She also translated and adapted popular songs into Hebrew, such as the Beatles song "Let It Be" in 1973.  In 1963, she composed ""Hurshat Ha'Eucalyptus"" ("The Eucalyptus Grove"), a song that evokes Kvutzat Kinneret where she was born. It was covered in a recent version by Ishtar. In 1967, she wrote the patriotic song, "Yerushalayim Shel Zahav" (Jerusalem of Gold), which was sung by Shuli Natan and became famous. She wrote it for the Israeli Music Festival. After Israel's victory in the Six-Day War that year, she added another verse celebrating the reunification of Jerusalem. The song "gained the status of an informal second national anthem."

Personal life.

She first married actor Gideon Shemer and had a daughter, Lali. They were later divorced. She later married an attorney, Mordechai Horowitz. The two had a son Ariel Horowitz, who also became a musician. Shemer continued to write her own songs. She died in 2004 of cancer, aged 73. Shortly before her death, she wrote to a friend, saying she had used a Basque folk melody as the basis for her 1967 "anthem," "Jerusalem of Gold". She had always denied it before. The friend and her family decided to publish the account. In 1962, singer Paco Ibáñez performed the Basque melody "Pello Joxepe" (Joseph The Fool), in Israel, when Shemer might have heard it.  Shemer was buried in the cemetery at Kvutzat Kinneret, her place of birth. Alongside her are buried many of the socialist ideologues and pioneers of the second and third waves of immigration. Shemer was buried near the famous Israeli poet Rachel, according to Shemer's wish.

Awards.

In 1983, Shemer received the Israel Prize for Hebrew song (words and melody).

Naomi Shemer (; July 13, 1930 – June 26, 2004) was a leading Israeli musician and songwriter, hailed as the "first lady of Israeli song and poetry." Her song "Yerushalayim Shel Zahav" ("Jerusalem of Gold") written in 1967, became an unofficial second anthem after Israel won the Six-Day War that year and reunited Jerusalem.

Naomi Shemer, née le à Kvoutzat Kinneret et morte le à Tel Aviv-Jaffa, est une auteur-compositrice israélienne. Elle est réputée pour ses talents de poésie, d'écriture, de composition, de mise en musique des textes d'autrui et d'adaptation en hébreu de chansons en langue étrangère.