How the Romans built their roads, and some curious things about their most famous highways

The Roman Empire would not have become what it was without its extensive network of highways.  Some of these roads, created more than 2,000 years ago, are still the basis of highways that we use today.


The Romans believed that the roads that connected the provinces and cities of the Empire were a crucial element in their political and military strategy. With the result that, as explained on the Aquis Querquenis website, the construction of these highways always reflected a careful strategy that usually came out of Rome. Indeed, the authors of that blog think it would be a “historiographic error” to accept the theory that associates the construction of highways with just military campaigns.


“The military engineers did make individual constructions –for example bridges to cross rivers that they then dismantled– for certain tactical movements during a battle, but commercial roads should always be associated with a political kind of planning,”  they note.


The fact that the decision to construct one of these so-called Viae Publicae (public ways) came down from the very center of Imperial political power gives us an idea of the large size of such works, which in most cases required the deforestation of the area through which the road would run.


The mensors were the professionals who determined the most appropriate placement of the road depending on the terrain. Their work was very similar to that of today’s surveyors. According to Aquis Querquenis, the incline should not have been steeper than 8% so as to facilitate the movement of vehicles pulled by animals, especially when they were carrying loads.


Once the vegetation had been cleared away, workers excavated the earth until finding a solid base. Then the ground was smoothed out and the width of the road was determined –usually between six and 12 meters– and stone was cut to form the edges.


Often huge rocks were used to establish the bottom layer, because they were capable of supporting all the weight of the vehicles that used the road.


Atop that base there was another layer formed by a mix of smaller, more arid stones to fill up any spaces. As explained by Isaac Moreno Gallo, an historian specializing in ancient and modern civil engineering, the top layer of the road consisted of the so-called zahorras, made up of sand, gravel and clay. The highest quality materials were used to guarantee the greatest possible durability.


The historian explains that once there was a compact top layer, the wagons, pulled by beasts of burden, advanced along the road to unload materials for the next layer. These materials were then extended using some planks of wood.  Then the materials were watered and finally further compacted by some rollers, usually pulled by animals. 


A Roman road crossing the Gredos mountains of Spain heading upwards towards the distant blue horizon. Concept of a road to nowhere, or towards the future.

To prevent water from forming puddles in the pavement, the roads usually had a slight incline on both sides so that rain water could run off. One of the curiosities recently discovered by Isaac Moreno are what is called beaconing gutters, a kind of continuous pit dug some 20 meters from the road on both sides of it. Among other functions, it kept the road from being invaded by wild animals and impeded the actions of any robbers.


But this isn’t the only curious thing about Roman roads. Here are a few more facts about their most important highways:


A Roman road crossing the Gredos mountains of Spain heading upwards towards the distant blue horizon. Concept of a road to nowhere, or towards the future.

. The first large Roman road was the Appian Way. It was ordered built in 312BC by the censor Appius Claudius Caecus Claudio Caeco to link Rome and Capua. It was 8 meters wide and more than 540 kilometers in length.


.  As the network of Roman roads grew ever longer, the so-called mansios were built beside them, predecessors of the later inns. They were used by travelers for resting up and were managed by the Roman government.


.  Lacking Google Maps or indeed road maps of any kind, the most reliable source of information about the highways was provided by the Antonine Itinerary. It was a document that was apparently updated from time to time and contained detailed information about the Empire’s roads. In it, these highways are identified by a number, beside which appeared the name of the city of origin and that of the destination, the length in miles of the road and, on some occasions, the most important intermediate cities and stops along the way.


. These Roman roads usually did not have curves. According to historians, the reason was that practicality that characterized the Romans. In this case, although they knew how to engineer curves, they preferred short stretches of straight lines that changed direction according to the needs of the terrain: straight stretches permitted a better visualization of the signaling beacons.