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All Roads Lead To Rome: Ancient Roman Highway Technology
David Geoffrey Smith, P.E., P.L.S.

While the Scanner typically features articles about modern breakthroughs and futuristic marvels of highway engineering and technology, it is also always interesting to look toward the past for inspiration and to recognize the vision and ingenuity of our forebears.

According to family history, one of my ancestors living over 1,600 years ago was a fellow named Flavius Afranius Sygarius, “The Wild Boar.” At the culmination of a lengthy political career he was appointed to serve as Consul to Lyons in Roman Gaul by Emperor Gratian in 382 AD. It is amazing to consider the state of highway engineering during the days when he looked upon the landscape. It has been said that one key to the success of the ancient Roman Empire was its efficient highways. The Roman highway system allowed speedy movement of troops, trade caravans, diplomats, and couriers; enabled rapid expansion of the Roman sphere of influence; offered military protection from barbarians and other invaders to local governors; allowed farflung outposts to stay in close contact and communication with the centers of government; allowed citizens to prosper through trade; and a host of other benefits.

Ancient Romans had highway administration systems similar to our Federal Highway Administration and state Departments of Transportation. Like our modern highways, Roman roads likewise had different levels of classification in terms of usage, maintenance and funding. These classifications in order of priority from highest to lowest were:

  • viae publicae (major public roads, funded by the Empire),
  • viae militarus (military roads, with the army as responsible party),
  • actus (local/regional roads, primarily funded and administered by the local Governor), and
  • privatae (privately funded roads).

The earliest and most well known of these Roman highways is the Via Appia, or Appian Way, running from Rome to the Bay of Naples, constructed around 300 BC. Like modern highways, ancient Roman roads like Via Appia, Strata Montana, Via Aurelia and others made up a vast network of highways and local roads. The network was extremely well coordinated and extensive. At the height of the Roman Empire, with use of sea ferries, Sygarius could have traveled continuously on Roman highways from the northwestern limit of the Empire at the Antonine Wall in northern Britain, across the Channel to France, through his city of Lyons, and then onward to Rome, Byzantium, Antioch, eventually ended his journey in Jerusalem at the southeastern extent for a distance of over 4,070 Roman miles, or approximately 3,740 U.S. miles (see table 1). Naturally, as the center of power, Rome was the hub of it all. As they say, “All Roads Lead To Rome.”

Although Roman surveyors were extremely skilled and could lay out accurate curves, Roman roadways typically are linear. This was due to the use of sighting techniques, which naturally resulted in very long tangents. This is most noticeable in the fact that Roman roads make most of their key turns and deflections on high ground where sighting was most easily facilitated. Road segments would often be laid out with series of hundreds of sighting points and beacons.

Before electronic traffic counters and modern concepts of axle loadings, the Roman highway engineer would use his years of e m p i r i c a l observations of local custom and traffic, as well as knowledge of local soils and geology to determine the ideal roadway section.

There was no mandated typical section in Roman highways, however the majority were constructed on an earthen embankment, called an agger, which would provide a welldrained base. On important routes, this agger could be constructed as high as 6 feet above the surrounding terrain, and 40 to 50 feet in width. This agger would typically be constructed of locally excavated earth and stony rubble, called statumen, and placed directly on level ground or within an excavated trench or then built up.

Material for the agger would often come from scoop ditches, excavated to either side of the proposed embankment, which would also aid in intercepting stormwater and for providing drainage. Scoop ditches were on occasion so extensive that they were in fact quarry pits providing roadway stone.

Upon this embankment, the agger, would be constructed a middle layer of finer material, called the rudus, which would be rammed down and compacted. Upper layers would be laid very carefully to maximize compaction. The middle layer would often contain sand and similar fines. The uppermost layer would be the “metalling,” a wearing surface, typically paving stones, as locally available within a few miles. At a bare minimum this would consist of gravel, however often cobblestone pavers or stone slabs would be used. This finished grade would also typically feature stone curbs, to contain the paving stones and delineate the edges of the road. If interesting local materials were available, for example burnt lime or volcanic tufa, they would also be used to provide concrete-like wearing surfaces. In areas where there was an iron working facility, iron slag left over from manufacture would be incorporated into the upper course to provide an incredibly hard wearing surface.

Roman highways would typically be cambered for drainage, and would sometimes have intentional wheel ruts gouged into them to aid carts and wagons on potentially difficult stretches of road given rain-slick or icy conditions. Similarly, there were occasional grooves perpendicular to the roadway scored into the road to prevent horses from slipping.

Decrees by Augustus and others provided for roads varying in width dependent upon importance and function. The widest, most important roads, decumanus maximus, were approximately 40 feet wide, whereas country roads were often 20 feet wide, to allow passing or two lanes of travel in opposing directions. Minor roads were typically around 8 feet wide.

Roman highways also had a “right-of-way” or easement of sorts, which were strips of land to either side of the agger embankment and main drainage ditches, typically kept clear, where cultivation and building were forbidden. These clear zones may have served multiple functions, such as to prevent assault by unfriendly forces or highwaymen, or to provide an area for roadside grazing. Small, shallow ditches called boundary ditches served no apparent drainage function, instead typically delineated these clear zones. In Roman Britain, many of the major roads had a clear zone 84 feet wide, whereas smaller country roads had a clear zone of 62 feet.

Roadways were well signed and marked at every mile with a stone monument, of tremendous accuracy. Ancient Romans utilized a form of odometer, essentially a calibrated, geared mechanism attached to the wheel of a cart for measuring distances and setting mile markers. Mile markers were often monumental in themselves, many standing 6 feet tall, and bearing mileages to the next town and intermediate points, as well as dates and names of the builders.

Amazingly, many sections of the ancient Roman roads, like Via Appia and die Bergstraße are still to this day intact in one form or another, even after 2000 years of use, weather, neglect, political upheaval and other circumstances that often ruin a nation’s infrastructure. These ancient Roman highways were unparalleled in their design and construction until the 19th century. To place it all in a proper context and perspective, perhaps the lesson to learn is that even with 2000 years of technological advances such as aerial photography, GPS and laser-guided graders, there is still no substitute for vision, experience, and ingenuity in highway design.

Dave Smith is a Professional Engineer and Professional Land Surveyor specializing in highway design, GIS, surveying and mapping, and custom engineering and CADD software development. Over the past 18 years, Mr. Smith has been involved in a wide variety of surveying and engineering projects up and down the East Coast, from Delaware to Vermont. In addition to surveying and engineering, he has a wide variety of eclectic outside interests, such as history and archaeology. He is Past President of the North-East Penn Section of ASHE, and recently developed a website for the North-East Penn Section ( For further information, his email is

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