By Mark S. Kuhar
It is estimated that the Roman road network was about 250,000 miles long, out of which about 50,000 miles were paved with stone. Like arteries, these marvelous feats of engineering ferried goods and services rapidly and safely, connecting Rome, “the capital of the world,” to the farthest stretches of the empire, and facilitated troop movements to hastily assemble legions for both border defense and expansion. Encompassing both military and economic outcomes, roads were truly central to Rome’s political strategy.
After completing all the geodetic measurements and projections, the Roman surveyors marked the path of the future road using milestones. All trees, shrubs, and other vegetation that might interfere with the construction of the road were razed. Marshes were drained and mountains would be cut through, if needed.
The average width of an ancient Roman road was around 20 ft., although some large public roads could be much wider.
According to the writings of Mark Vitruvius Pollio, a Roman architect and engineer who lived in the first century C.E., Roman public roads consisted of several layers:
- Foundation soil. Depending on the terrain, builders either dug depressions on level ground or installed special supports in places where the soil subsided. The soil is then compacted and sometimes covered with sand or mortar to provide a stable footing for the multiple layers above.
- Statumen. A layer that was laid on compacted foundation soil, consisting of large rough stone blocks. Cracks between the slabs would allow drainage to be carried through. The thickness of this layer ranged from 25 to 60 cm.
- Rudus. A 20-cm-thick layer consisting of crushed rock about 5 cm in diameter in cement mortar.
- Nucleus. A concrete base layer made of cement, sand and gravel, that was about 30-cm thick.
- Summum dorsum. The final layer consisting of large 15-cm-thick rock blocks. But more often fine sand, gravel, or earth was used in the top layer, depending on the available resources at the workers’ disposal. This layer had to be soft and durable at the same time. Paved roads were very expensive and were typically reserved for sections located near and inside important cities. When pavement (pavimentum) was used, large cobblestones of basalt laval were typically used in the vicinity of Rome.
According to Ulpian, a second-century C.E. Roman jurist and one of the greatest legal authorities of his time, there were three major types of roads:
- Viae publicae. These were public or main roads, built and maintained at the expense of the state. These were the most important highways that connected the most important towns in the empire. As such, they were also the most traveled, dotted by carts full of goods and people traveling through the vast empire. But although they were funded by the state, not all public roads were free to use. Tolls were common at key points of crossing, such as bridges and city gates, enabling the state to collect import and export taxes on goods.
- Viae militares. Although Roman troops marched across all types of roads and terrain for that matter, they also had their dedicated corridors in the road network. The military roads were very similar to public roads in design and building methods, but they were specifically built and maintained by the military. They were built by legionaries and were generally closed to civilian travel.
- Viae privatae. These were private roads that were built and maintained by citizens. These were usually dirt or gravel roads since local estate owners or communities did not possess the funds nor the engineering skills to match the quality of private roads.
- Viae vicinales. Finally, there were secondary roads that lead through or toward a vicus or village. These roads ran into high roads or into other viae vicinales and could be either public or private.