How Did the Ancient Romans Manage to Build Perfectly Straight, Ultra Durable Roads?
September 1, 2019 Karl Smallwood
Marbleezy asks: How did the ancient Romans manage to build perfectly straight roads hundreds of miles long?
The ancient Romans were a people famed for their architectural prowess, something no better demonstrated than by their ability to build almost perfectly straight and incredibly durable roads spanning expansive distances. For example, in Britain alone, the Romans built well over 50,000 miles of roads with the longest ruler-straight stretch spanning over 50 miles. They did all of this in an era without modern surveying tools, construction equipment, or even very accurate maps of precisely where their destination was for many of the areas. So how did they do it?
To begin with, it's important to note there were a few different types of roads that were made throughout the Roman Republic and Empire, and exact method and materials used for road construction varied somewhat from region to region and evolved slightly over the centuries.
That caveat out of the way, the three main classification of Roman roads were viae terrenae, essentially dirt roads, often made by people walking and wagons riding over the same path over time; viae glareae, which would be a dirt road that was then graveled; and, finally much more interestingly, viae munita, which were more or less paved roads, some of which have survived through modern times.
Within these types of roads there were further classifications based on who could use them, such as viae publicae (public roads), viae militares (military or state use roads), and viae privatae (private roads, constructed at private expense and for the owners to decide who they allowed access, perhaps the general public or perhaps just a select few).
To help pay for them, roads of all types often had tolls, particularly at locations like bridges and city gates where it would be impractical to avoid the tolling location.
This brings us to the road construction process itself. As dirt and gravel roads aren't terribly interesting, we're going to focus this article on the viae munita. So how did they make these incredibly durable and generally amazingly straight roads? After all, even with modern machinery, constructing and maintaining an expansive road system is an extremely time consuming and labor intensive process.
To start with, a group of surveyors would be sent out to figure out the precise direction connecting the two main points. At the same time, they'd attempt to plan the route as efficiently as possible while accounting for any major obstacles like tall mountains, rivers, etc. When possible, they may attempt to avoid such obstacles, but, particularly in some of the earliest Roman road construction, where it might result in having to take a large detour to get around, say, a mountain, if possible given the terrain, they tended to just build the road to go directly over it or directly through it. For example, the longest tunnel through such a mountain was the Grotta di Cocceio which was excavated from 38 to 36 BCE and is approximately 1 km (.62 miles) long and about 5 meters (5.4 yards) high and wide. Before WWII, it was also still a fully functional and safe to traverse tunnel despite standing about 2,000 years at that point, but was damaged during the war, though there are presently efforts to have it repaired and opened again to the public.
As for going over a mountain, it's important to note here that we don't mean they'd use switch backs as is the general method today. No, if at all possible, they'd just build roads straight up a mountain and down the other side, expecting the soldiers and mules and the like to just man up and traverse the steep slopes without complaint.
That said, as the empire matured, it did eventually become apparent that there were economic advantages to slightly longer roads that were easier for draught animals to pull carts over, and thus there was a shift to favoring longer distances but lesser gradients when talking roads for general public use.
Either way, during the process, the surveyors would setup markers, often at very visible points like on hills, mapping out the optimal path, again trying to ensure the road would be as straight as possible between the start and end point to reduce needed labor, materials, and distance needed to traverse the road once it was complete.
This brings us to how they actually ensured perfectly straight roads between the markers. A key tool here was a device known as a groma. In a nutshell, this was nothing more than a sort of cross with four weights hanging from a string at each end of the cross to function as plumb lines. The whole thing could rotate with degree markers on top. Two of the plumb lines would then be lined up with a marker and then on the other side lined up with the previous marker. Where changes in direction would need to be made, the degrees were marked and ultimately the whole thing drawn up on a central document showing the entire route of the road with each segment.
Once the actual construction was to begin, the groma would once again be used, this time with rods pounded into the ground between markers using the groma to make sure every single rod was perfectly inline in between the markers.
Now, finally, construction of the road would start, usually first done via plows to loosen the soil, this would be followed by legionaries and/or slaves digging the ground out, with depth varying based on conditions. For instance, swampy land would need a lot thicker foundation if it was to have any staying power. For more typical ground, the trench needed would be somewhere in the realm of 3-6 feet (around 1-2 meters) deep. Once dug out, this would then be tamped down to a leveled, compact layer of earth.
From here, exact road composition varied based on available materials in a given region, land composition, and a variety of factors like this.
But typically large stones would be packed as tightly as possible together and into the earth base. Onto this layer would usually be placed smaller stones, sometimes comprising broken concrete or somewhat crushed rock, again packed and smoothed as best as possible. Depending on availability, they would also put a layer of sand on this foundation to make a genuinely perfectly smooth surface.
On top of all of this, at the minimum gravel would be added, packed, and leveled. In some cases, such as near big cities, as described in one manuscript on the construction of roads in Rome itself, paving stones, often flint, lava rock, or marble, would be embedded in cement for the top layer instead. When the road was complete, they are thought to have been quite smooth allowing for relatively bump free travel in carts and the like.
During this whole process, special attention was taken to making the center of the road higher than the sides so that any water would drain off, with the entire road surface itself also elevated above the ground on the sides where drainage ditches would generally be created to help rapidly move water away from the road in times of heavy rains.
As for the size of the roads, according to something known as The Law of Twelve Tables, which more or less formed the basis of Roman Law for almost a millennia, Roman roads were required to be at minimum 8 Roman feet wide (which converted into modern units equals about 2 and half metres) where the road was straight and double that if the road happened to be curved.
Beside the roads were footpaths, sometimes graveled, which were particularly handy in the case of viae militares where only people with proper authorization could use the road itself. Finally, at the very outer edges of the roads, any nearby trees and bushes would be removed to help reduce areas for bandits to hide and surprise anyone with an attack, as well as to help ensure plant growth didn't overtake the road or tree roots compromise it.
But this wasn't the end of the construction process. They now needed to know exact distances along the road. It's not fully clear how they did this, though a device known as the odometer of Vitruvius is mentioned starting around 27 BC and is often claimed to have been used for this purpose. However, whether it was actually ever used for road construction, or even made at all, is up for debate.
At a high level, this device used the spinning of a wheel to mark distance. In this case, it was the spinning of a wagon wheel which was in turn hooked up to gears that would drop a pebble into a container every Roman mile (4,841 feet, which is around 1,000 paces of an adult male, with the world "mile" deriving from the Latin milia, meaning, funny enough, 1,000 paces).
For whatever it's worth, while Leonardo da Vinci tried and failed to make such a device as per outlined, in 1981 one Andre Sleeswyk was successful in building one exactly as described except, unlike da Vinci, he used triangular gear teeth instead of square ones. His justification for this modification being that these same type of gear teeth were used in the Antikythera mechanism, which was created sometime from around 250 BC to 70 BC, with the device itself used to predict various astronomical phenomenon like eclipses. Thus, perhaps if the odometer of Vitruvius was ever actually built and used, maybe it used these too.
There are, of course, many other much less technologically advanced ways they could have measure mile distances easy enough and with extreme accuracy. However they did it, at every mile mark, the law required they place an approximately two ton, 7 foot tall (2 feet in the ground) mile marker, called a miliarium. Helpfully, on this stone would be engraved the names of the locations the road connected and how many miles to each from that respective marker. A master marker, known as the Miliario Aureo or Golden Milestone was also created during Caesar Augustus' rule and placed in the central Forum of Rome itself. This was the point at which all Roman roads were said to lead. It's not actually clear what was on this master marker, but it's been speculated it listed the distances from that point to all major cities under Roman rule.
Whatever the case, like the roads themselves, some of these mile markers are still standing giving archaeologists and historians a valuable snapshot of the past, since they tended to include not just basic geographic information, but information about when the road was built or repaired and by whom.
Next up, it was also required by law that regular way stations be built for official use, generally every 16 to 19 miles apart. These were more or less really nice resting areas providing food and drink and the like for officials. For the general public, inns known as cauponae would tend to pop up near these way stations. On that note, at particularly high trafficked way stations, many other businesses would pop up as well, sometimes leading to the creation of whole towns.
Along these roads you'd also find at similar intervals mutationes, or changing stations, where people could get the services of veterinarians, wheelwrights, etc., as well as potentially find new mounts.
To give you an idea of how fast one could move along these roads with its network of way stations and facilities, it's noted that Emperor Tiberius once traversed about 200 miles in 24 hours after news that his brother, Drusus Germanicus was dying from gangrene after being seriously injured falling from a horse. A more typical time to traverse for, say, a government mail carrier was usually around 50 miles per day if not in a particular hurry.
But to sum up, it turns out that Roman road construction, amenities and all, wasn't all that different from modern times, often featuring deep foundations, paved surfaces, proper drainage, landscaping around the roads, sidewalks, toll booths, rest areas, hotels, restaurants, the historic equivalent to gas stations and convenience stores, etc.
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Bonus Fact:
The infamous phrase—"Nero fiddled while Rome burned"—has come to mean a person who is neglecting their duties, probably by doing something frivolous. But did Nero actually sit around play music while Rome was burning around him in 64 AD?
To begin there was such a fire, though its extent is unknown. According to Tacitus, the fire lasted for six days and decimated Rome, with only four districts untouched (out of a total of fourteen). He goes on to state that ten of the eleven districts that burned were heavily damaged, with three of those completely destroyed. However, oddly, there is very little documented mention of the fire from those who actually lived through it. The only Roman historian during that period who even mentioned it at all was Pliny the Elder, and even he only briefly referenced it in passing.
Had it been as widespread as Tacitus claimed, one would think the likes of Plutarch, Epictetus, or other such famed Roman historians who lived through the fire would have mentioned such a significant event. And, indeed, we see that perhaps it wasn't that great of a fire from the only other documented first hand account of the scope of the disaster- a letter from Seneca the Younger to Paul the Apostle, where he explicitly stated that only four blocks of insulae were burned (a type of apartment building), along with 132 private houses damaged (about 7% of the private houses in the city and .009% of the insulae). Not anywhere close to as widespread as Tacitus later claimed, though Seneca did say the fire lasted six days, as Tacitus stated.
As to Nero's reaction to the fire, the first and biggest flaw in the fiddling story is that the fiddle, or violin, didn't actually exist in Nero's time. Historians aren't able to give an exact date for the invention of the violin, but the viol class of instruments to which the violin belongs wasn't developed until at least the 11th century. If Nero actually did play a stringed instrument—and there's no evidence that he did, whether during the burning of Rome or otherwise—it was probably a lyre or cithara.
Okay, so some details can get muddled through history. But did Nero neglect Rome while it burned? Historians argue probably not. Reports do place Nero thirty-five miles away from Rome at the time of the fire, as he was staying in his villa at Antium. However, an account from Tacitus tells us that he returned to Rome immediately when word of the fire reached him in order to begin relief efforts. As the fire raged on, Nero even opened up his own gardens to provide a temporary home for those who were now homeless. He also ordered the construction of emergency accommodation and cut the price of corn, as well as provided food directly, so that people could eat. Besides this, he paid for much of these relief efforts out of his own pocket.
However, Tacitus also tells of the rumour that had spread among the masses: while the flames surged through the city, Nero stood on his private stage and sang about the destruction of Troy in a comparison of the two events. Whether or not the rumour had any evidence to back it up or was just something made up by the unhappy masses, we don't know, but this and Suetonius' account are the most likely source of the fiddle story we hear today. Unfortunately for Nero, at least in the context of this story, he did have a reputation for enjoying concerts and participating in music competitions, so the activity itself wasn't entirely unlikely even if the timing of the act is highly questionable.
While Tacitus claims the singing story was a rumour, Suetonius wrote about it with conviction. However, the story could have been an attempt to further mar Nero's name. Nero faced problems during his reign from the very start, when it was reported that his own mother poisoned his predecessor, Claudius. He was also blamed for the death of Claudius' son Brittanicus, who was being urged to take his proper place as Emperor by overthrowing Nero. Numerous other deaths were thought to have been committed by Nero's hand, including one of his wives and his own mother.
As such, Nero was painted as a man who was difficult for the masses to trust. No one knew how the fire started, and many Romans believed that he had started the fire that burned their city. (It likely started in shops containing flammable goods, and was probably an accident rather than any one person's intentional act.)
With the mob out for blood, Nero was forced to turn to a scapegoat and blamed Christians for starting the fire. There were only a small number of Christians in Rome at the time and they were considered a strange religious sect, so they were an easy target. As Tacitus stated:
Consequently, to get rid of the report, Nero fastened the guilt and inflicted the most exquisite tortures on a class hated for their abominations, called Christians by the populace. Christus, from whom the name had its origin, suffered the extreme penalty during the reign of Tiberius at the hands of one of our procurators, Pontius Pilatus, and a most mischievous superstition, thus checked for the moment, again broke out not only in Judæa, the first source of the evil, but even in Rome, where all things hideous and shameful from every part of the world find their centre and become popular. Accordingly, an arrest was first made of all [Christians] who pleaded guilty [to the fire]; then, upon their information, an immense multitude was convicted, not so much of the crime of firing the city, as of hatred against mankind. Mockery of every sort was added to their deaths. Covered with the skins of beasts, they were torn by dogs and perished, or were nailed to crosses, or were doomed to the flames and burnt, to serve as a nightly illumination, when daylight had expired.
Even finding someone to blame for the fire didn't help Nero's plea of innocence. In the wake of the fire, he built a palace on top of some of the land cleared by the flames, which people argued he had been planning from the start, though this is highly unlikely as the place he built the new palace was over a half mile away from where the fire started. In addition to a new palace, Nero did provide for the reconstruction of the city, but rebuilding stretched the limits of Rome's treasury at the time. He was forced to devalue Roman currency, which wasn't a popular move.
Nero ended up committing suicide—or at least, begging his secretary to kill him when he lost the nerve to do it himself—four years after the fire. Accounts of his life and of the time of the fire are highly contradictory. Further, Suetonius and Tacitus wrote their histories fifty years after Nero died, and Cassius Dio wrote his 150 years later. Many historians also think it likely that Nero was more popular with the people of Rome than he was with the senators, and as all three of the main sources were from the senatorial class, it's likely they carry more than a little bias against him, not unlike happened with the popular history of Marie Antoinette who popular history remembers very differently than who the actual woman appeared to be. That being said, Tacitus did state that while Nero's death was welcomed by senators, the lower classes mourned his passing.
So in the end, the implication that "Nero fiddled while Rome burned"—or played the lyre, sang a song, or neglected his duty in any way—is likely the result of anti-Nero propaganda and an attempt to tarnish his name. The morality of many of his actions during his reign is open to debate, but the fiddling, or playing music, story is almost certainly a myth, unless he was playing to entertain the displaced masses he'd taken in.
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Nero Fiddling While Rome Burned
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Odometer History
Antikythera mechanism
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calbadger
Great article. I truly enjoyed the writing and the detail. However you misuse a word from Latin, "decimated." As I'm sure you know, that means one in ten, based upon the Roman Army's punishment for large groups of troops that broke and ran in large numbers. Perhaps "devastated" could be substituted?
[I have already noted several more of your articles that I wish to read as well.]
Daven Hiskey
Thanks! As for decimated, while it is true that was once the definition, starting all the way back in the 17th century the "kill/destroy" definition started popping up and became quite common in the 19th century and on through to today (according to the OED). As for today, Oxford gives the following definitions for decimate: "to kill large numbers of animals, plants or people in a particular area. To severely damage something or make something weaker" Websters includes, among other definitions: "to cause great destruction or harm to."
I've always understood the word "fiddled" to mean touch or fidget with something in a restless or nervous way. It would never have occurred to me that Nero would be playing an instrument…just killing time in a wasteful way.
How could Nero cut the price of corn, when corn wasn't brought to Europe until contact with the Americas?
Corn has long been just a general word for grain throughout Europe. It's actually why maize is called corn in America.
Aren't the majority of your users American, or using American English? If that's the case, why not just call it "grain," a term that's unambiguous for all English speakers?
The distinction might seem pedantic to others, but I have a food science background along with a keen interest in the origins of our food. I want the layman to know that corn (maize) is an innovation of the Mesoamerican people. We tend to forget about their many contributions to our lives, which is a bummer.
As the letters of Seneca to Paul are seen as forgeries by modern scholars, I find it weird that you use it as a source, especially without questioning its validity. I expected better from you.