Roman Roads and Transportation: The Arteries of Empire

The Roman road network was the largest and most durable public works project of the ancient world. By the time of the empire, more than 80,000 kilometers of paved highway stretched from the Atlantic coast of Spain to the Euphrates, from the Scottish Highlands to the Sahara. The roads were the arteries along which the legions marched, the imperial couriers rode, the merchants drove their carts, and the imperial tax revenues flowed. They were the first modern transportation system, and the engineering principles that built them are still the basis of highway construction. For the broader context, see Roman Engineering and Architecture.

The Roman road system was not planned as a single network. It grew out of the practical needs of a small Italian state that was constantly at war with its neighbors. The first Roman roads, the Via Appia and the Via Salaria, were built in the fourth century BCE to connect Rome with its allies in central Italy, and the network was extended across Italy as the Republic conquered the peninsula. After the conquest of Gaul and Spain in the first century BCE, the network was extended to the Atlantic, and after the conquest of Britain in 43 CE, it crossed the Channel. For the wars that produced much of the network, see the Punic Wars and famous Roman battles.

The 80,000-Kilometer Network

The exact length of the Roman road network at its height is unknown. The figure of 80,000 kilometers of paved road is a modern estimate, based on the surviving remains and on the itineraries — the maps and route lists — that have come down to us. The real length, including unpaved military and local roads, was probably much greater. The most important routes, the viae publicae, were paved highways maintained by the state, with a total length that historians estimate at between 80,000 and 100,000 kilometers.

The network was organized around a set of great trunk roads. The most important was the Via Appia, the “Appian Way,” which ran from Rome southeast to Capua, Beneventum, and Brundisium, the port of departure for Greece and the east. The Appian Way was begun by the censor Appius Claudius Caecus in 312 BCE and was the first of the great Roman roads. The Via Appia, sometimes called the “regina viarum” — “queen of roads” — was extended to Brundisium in 244 BCE and still exists in parts today. For more, see What Was the Appian Way?.

Other important trunk roads included the Via Aurelia, which ran northwest along the coast of Etruria to Gaul; the Via Flaminia, which ran north from Rome to Ariminum (modern Rimini) and on to the Danube; the Via Cassia, which ran to Arretium (modern Arezzo) and on to Florence; the Via Salaria, which ran east from Rome to the Adriatic through the salt-producing country of the Sabines; the Via Egnatia, which ran east from Brundisium across northern Greece to Byzantium (later Constantinople); and the great Via Domitia in southern Gaul, which connected Italy with Spain. For the network in a specific province, see Roman Britain, which was crossed by a remarkable system of military roads including Watling Street and Ermine Street.

Construction in Layers

A Roman road was one of the most carefully engineered structures of the ancient world. The standard cross-section, used on a remarkably consistent pattern from the second century BCE to the second century CE, had four layers, from the ground up:

The first layer, the statumen, was a bed of large stones, often 25 to 60 centimeters in diameter, laid in the excavated trench. The stones were laid in such a way that they touched each other, and the gaps were filled with smaller stones.

The second layer, the rudus, was a layer of crushed stone, often mixed with lime mortar, compacted to a depth of about 25 centimeters. The rudus was the structural layer of the road, and it distributed the load of the surface.

The third layer, the nucleus, was a finer layer of concrete, made of gravel, sand, and lime, compacted to a depth of about 30 centimeters. The nucleus was the actual surface of the road, and the cement bonded the layer above it to the layer below.

The fourth and topmost layer, the summum dorsum, was the surface paving. It consisted of large polygonal paving stones, often basalt, fitted closely together. The surface was crowned — slightly higher in the center than at the edges — so that water would run off to the ditches that flanked the road.

The total thickness of the road was often as much as 1.5 meters, far more than was strictly necessary. The over-engineering was deliberate: a road built to this standard would last for centuries, and many of the most heavily trafficked Roman roads are still in use as the foundations of modern highways. The Appian Way outside Rome is still visible today, two thousand years after it was first laid, with the ruts of Roman wagons cut into its paving stones.

The Romans understood the importance of drainage. Roads were laid on a slightly raised embankment, with gutters and culverts at the sides to carry off rainwater. The road was crowned, as noted above, with a typical camber of 1:30 to 1:60, so that water would run off to the sides. Many of the bridges of the Roman road system were stone arches that have stood for two thousand years, and many of the smaller culverts were made of brick-faced concrete. For the technology that made all of this possible, see What Was Roman Concrete?.

Milestones

The most distinctive feature of a Roman road was the milestone, the miliarius, that stood beside it at regular intervals. Every Roman mile, the mille passus, was 1,000 Roman paces, about 1,480 meters or 0.92 modern miles. Each milestone was a cylindrical column of stone, with the distance from the nearest major city carved on its face, and often an inscription commemorating the emperor or local official responsible for the road.

The milestones were not just markers. They were also propaganda, publicizing the emperor’s name and titles and reminding every traveler of the imperial government’s investment in the road. The surviving milestone from Brescia in northern Italy is a typical example: it records that the emperor Vespasian ordered the road repaired in 74 CE, and lists the names of the local magistrates who supervised the work.

The milestones also gave the Romans an idea of their own empire. A famous funerary monument from Padua, the tombstone of the veteran Titus Vinius, records the survivor’s services in the legions and lists the cities he had passed through, beginning with Brundisium and ending with Londinium — the first map of Roman Britain drawn by a Roman soldier.

The Cura Viarum

The Roman road system was managed by the cura viarum, the “care of the roads.” The earliest cura viarum was the office of the censors, who supervised the construction and repair of the public roads. Under the empire, the cura viarum was reorganized and entrusted to a new class of officials. The most important was the curator viarum, a senator of praetorian rank who was responsible for the roads of a particular region. The most important of all the curae was the curator a lariciis, the “commissioner of the larches,” who supervised the timber supply for road and bridge repairs.

The road maintenance was financed by a special fund, the pecunia viaria, the “road money,” drawn from the imperial treasury. The maintenance work was performed by military units — legions stationed along the road were responsible for the upkeep of the road in their area — and by contractors, who bid for the work in a public auction.

Bridges

The Roman road network required bridges, and the Romans built some of the most remarkable bridges of the ancient world. The earliest Roman bridges were simple wooden structures, but as the empire grew the bridges were built of stone and concrete, often with arches of 30 meters or more. The longest surviving Roman bridge is the Limyra Bridge in southern Turkey, with 26 arches stretching 360 meters across the Gökçayır stream.

The most famous Roman bridge is the Pont du Gard in southern France, a three-tiered aqueduct bridge over the Gardon River. Although it is technically an aqueduct bridge rather than a road bridge, it is a perfect example of the Roman mastery of stone arch construction. For more, see Roman Aqueducts and Water Systems.

Vehicles

A Roman road was built for the wheeled traffic of the Roman world. The most common vehicles were the raeda, a heavy four-wheeled wagon used for freight; the carruca, a lighter four-wheeled carriage used for passenger traffic; the cisium, a light two-wheeled gig; and the birota, a two-wheeled cab. The largest of the freight vehicles could carry loads of up to a ton, and a typical Roman freight wagon had its axles and wheels of standard size, so that spare parts could be interchanged. The ruts cut into the paving stones of the Appian Way outside Rome are spaced 1.4 meters apart, the standard gauge of a Roman freight wagon.

The Roman authorities regulated traffic. The speed limit in built-up areas, at least in theory, was limited to walking pace. The emperor Tiberius reportedly fined a praetorian prefect for speeding through Rome in a heavy wagon. Goods wagons were not allowed on the streets of Rome during the day, when the population was most active, and deliveries were restricted to the night hours.

The Postal System: The Cursus Publicus

The most important institution that used the Roman roads was the cursus publicus, the “public postal system.” The cursus publicus was a state-supplied and state-maintained transport system, used for imperial correspondence, official travel, and military logistics. It had been set up in something like its final form by the emperor Augustus, and it was the model for the postal systems of the medieval and modern states.

The cursus publicus worked through a system of mansiones (inns) and mutationes (horse-changing stations) along the main roads. The mansiones were typically twenty-five to thirty kilometers apart — about a day’s journey by foot or by cart — and they provided lodging for imperial officials and a stable for the animals of the relay. The mutationes were typically ten to fifteen kilometers apart, where a fresh horse or mule could be obtained. The animals were kept in imperial studs, the equorum copia, and the personnel were government employees, the muliones (mule drivers) and the hippocomi (horse handlers).

The cursus publicus was not free for general use. A special pass, the diploma, was required to use it, and the pass was issued only to imperial officials, senators, soldiers, and a small number of privileged private individuals. The system was expensive: the cost of maintaining the mansiones, the mutationes, and the imperial post was a major item in the imperial budget. The emperor Hadrian tried to reform the system, restricting the issuance of diplomas, and the emperor Diocletian again tried to limit it. For the political context, see Diocletian and the Tetrarchy.

The Roman courier, the tabellarius, was one of the great heroes of the imperial administration. The tabellarius could cover a hundred kilometers a day on a fresh horse, and the imperial news, the acta — including the daily edicts of the emperor, the records of the Senate, and the news from the frontiers — was distributed across the empire through the mansiones. The Roman courier was, in the third century, replaced by the imperial courier of the Tetrarchy, and in the late empire, by the cursus velox and the cursus clabularius, the rapid and the slow services.

The Legacy of the Roman Roads

The Roman road system was the most important piece of physical infrastructure of the ancient world. It allowed the Roman army to move with unprecedented speed across the empire. It allowed the imperial tax system to collect grain and silver from the provinces and bring them to the capital. It allowed the imperial postal system to send orders and receive information. It allowed the merchants of the empire to move goods, and it allowed the imperial culture of law, language, and religion to spread.

The roads were also the most durable legacy of the empire. Many of the Roman roads in Europe, North Africa, and the Middle East remained the principal routes of travel long after the empire had fallen. The Appian Way, the Flaminian Way, the Cassian Way, and the Egnatian Way were the principal roads of Italy and the Balkans for more than a thousand years after the fall of Rome. The French road system, the voies romaines, was the basis of the routes nationales of the nineteenth century. The British trunk road system — the Fosse Way, the Watling Street, the Ermine Street — was the foundation of the A roads of the modern motorway system.

The roads are also a reminder of how the Roman Empire worked. The Roman Empire was, in the end, a logistical operation. It succeeded because the Romans were able to feed, equip, and pay their armies, and they were able to do that because they had built the roads along which the supplies could move. The fall of the Western Roman Empire was, in part, the fall of the road system. The empire had grown too large, the legions too thinly stretched, and the cost of maintenance too high, and the western roads slowly reverted to local tracks, while the eastern roads, maintained by the surviving eastern empire, continued to carry traffic for another thousand years.