Roman roads were vital to the functioning of the Roman state.
They enabled the fast and efficient movement of armies, tradesmen, officials, animals and goods between key urban and rural locations, ranging from small rural villages to the largest cities in the Empire.
At the height of its power, no fewer than twenty-nine great military highways radiated from the capital, and as many as 372 major roads connected the late Empire’s 113 provinces.
Overall, more than 250,000 miles (400,000 kilometres) of roads connected the many centres of the Roman Empire, of which 50,000 miles (80,500 kilometres) were stone-paved.
The construction of Roman roads was an extraordinary feat of planning, skill, and material wealth, and enabled the Empire to grow in power for centuries. There were three types of road in the Roman period: Viae publicae, Viae privatae and Viae vicinales.
The first was equivalent to our typical modern day motorway, the second akin to our modern-day A road, and the third not unlike our modern B roads. Each was laid along accurately surveyed routes, occasionally traversing through or over hills, while others were constructed over rivers and ravines using bridgework.
Major Roman roads were built to withstand high volumes of traffic, including wheeled vehicles, animals, and individuals on foot. As such, they were often stone-paved and metalled.
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They were also commonly cambered to allow drainage and flanked by footpaths, bridleways and drainage ditches. In all cases, their construction was a well-oiled process involving engineers, constructors, animals and vehicles, and an expression of Roman efficiency at its best.
Roman Roads Construction Process
The mapping and construction of Roman roads, like many aspects of Roman life, was an efficient process. The average construction rate per man per day was just over one by five metres, and many officials, workers and slaves were involved in their erection.
Once an area was chosen, constructors, often slaves, soldiers, or convicts, would get to work de-foresting in order to remove all vegetation. In the strip that had been created, the topsoil would then be dug out until a solid base was established.
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At the same time, three-foot trenches and small retaining walls or kerbs would be dug out and constructed along the edges of the new route at a width appropriate to the chosen road. Most Roman roads were wide enough to allow two animal-drawn carts to pass one another comfortably.
20 Pedes
As such, the most common width of a Roman road was around 20 pedes, or feet, wide. This is the equivalent to just under two standard lanes in the UK, which measure around 12 pedes in width. On top of the mortar or levelled earth, workers would establish the foundation layers of the road.
1 Native earth, levelled and, if necessary, rammed tight
2 Statumen: stones of a size to fill the hand
3 Audits: rubble or concrete of broken stones and lime
4 Nucleus: kernel or bedding of fine cement made of pounded potshards and lime
5 Dorsum or agger viae: the elliptical surface or crown of the road (media stratae eminentia) made of polygonal blocks of silex (basaltic lava) or rectangular blocks of saxum qitadratum (travertine, peperino, or other stone of the country).
The upper surface was designed to cast off rain or water like the shell of a tortoise. The lower surfaces of the separate stones, here shown as flat, were sometimes cut to a point or edge in order to grasp the nucleus, or next layer, more firmly
6 Crepido, margo or semita: raised footway, or sidewalk, on each side of the via
7 Umbones or edge-stones
Gravel Cemented
This was commonly made up of rocks and usually layered with gravel cemented with lime mortar to fill the gaps. For the final layer, blocks of stone, iron ore, or volcanic lava would be arranged neatly. Alternatively, more gravel, sand, or clay would be laid out to create a smooth finish.
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Tipper carts would move along the already compacted layers to distribute materials for the next layer. After tipping the carts up, the material would need to be spread smoothly and evenly with planks attached to further horses, much in the function of a plough.
Following these horses, water from barrels would wet the road material before it was further compacted with rollers. All such materials were once again transported and operated with the use of horses.
Drainage
This continuous process allowed the efficient and quick construction of roads. The final geometry of the roads had slightly sloping sides and ditches to allow rainwater to move downwards and to the edges. This was especially the case in rainy regions where roads were often constructed on raised embankments or linear mounds known as “aggers” to prevent flooding.
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More recently, archaeologists have discovered that ditches were dug twenty metres on either side of the road to prevent access by vehicles unauthorised to drive on them.
The distance at which these were placed also increased the peripheral vision of travellers, allowing them good warning for any unwanted ambushes from highway robbers or wild animals.
Examples of Roman Roads
The Appian way is probably the most famous road from the Roman period. At its peak, the road ran 400 miles from Rome in the centre of Italy to Brindisi in the south. It is now considered to be the world’s first super highway. Today, it provides a good case study of how durable roads were created by the Romans over 2,000 years ago.
To construct the Appian Way, workers excavated parallel trenches at a distance of roughly 40 feet apart to mark the location of the road and establish the nature of the subsoil.
Above this foundation, a light bedding of sand and mortar was laid, before four main courses.The first of these was a statumen layer made up of large flat stones, ranging between 10 and 24 inches thick. On top of this came the radius course, consisting of smaller stones mixed with lime.
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This measured around 9 inches thick. The third main layer was called the nucleus and measured around one foot thick. This was made up of concrete and small gravel, as well as coarse sand mixed with hot lime and water.
Flints
Finally, the summa crusta, or wearing surface, was constructed from flint-like lava stones which were fitted tightly together in an interlocking fashion to create a compact and even surface. This measured around 6 inches thick.
The final product was a compact and hardy surface built to withstand the high volume of cart and foot traffic traversing its length every day.
Looking elsewhere in the Empire, we can see more evidence for the planning processes behind the construction of streets and roads. In AD 79, the eruption of Mount Vesuvius covered and preserved the town of Pompeii and other surrounding settlements, leaving behind buildings, art, objects, and skeletal remains for archaeologists to examine today.
Preserved Roads and Streets
In addition, the complex street network of the town was almost perfectly preserved, including the street fountains, stepping stones, and wheel ruts left by horse-drawn carts.
Archaeologists and historians have spent decades studying the streets of Pompeii. They have discovered much about Roman steering systems from the markings left behind.
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The streets of Pompeii were built to withstand a high and frequent flow of pedestrianised and wheel-based traffic. The streets were narrow, with around eighty percent being limited to a single lane, while the kerbs were high, measuring over 30 cm on average.
In addition, Pompeii boasted more than twenty times more crossing stones than any other Roman city, at a current total of 316 (not including those so far unexcavated).
The combination of these factors shows a street plan designed to contain the constant flow of aqueduct water overflowing from street fountains, roof runoff from rainfall, broken pottery, and sewerage, and for organising the busy movement of pedestrians, animals, and cart traffic.
City Walls
There were no traffic signs in Pompeii so traffic had to be managed by those who constructed them, and those who drove on them.
Entering Pompeii from outside of the city walls, one would enter on a two-lane street and be faced with the decision fairly quickly to turn onto a one-lane (and thus often one-way) street, which was both confined and had reduced directionality.
These one-lane streets were common; 77% of the streets in Pompeii are one lane wide, meaning that traffic jams and wagon-on-wagon stand-offs were highly likely. Carts would trundle over the large stone paving slabs, straddling the crossing stones made for pedestrians, and turn around corners, leaving deep furrows over time in the stone below them.
On some streets barriers, such as fountains and stones, prevented wagon access entirely in certain streets and alleys. In recent excavations in Region V of the town, in a triangular “wedge” shaped area between the houses of Nozze d’Argento and Marco Lucrezio Frontone, a Roman street which was under construction when the eruption hit was uncovered.
Subgrade
On the (now named) Vicolo dei Balconi in AD 79, the laying of compact lava stone flags was interrupted about halfway from north to south, preserving the processes described above in great detail.
Below the large flagstones, the preparatory subgrade for the street had already been laid, ready for the top layer. More secrets will undoubtedly be uncovered in future analysis of this road, undoubtedly providing more important insights into the design and construction techniques used by the Romans in Pompeii and, as we have seen, the Empire overall.
