LiDAR Reveals an Ancient Roman Highway

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The mountainous, limestone landscape near Trieste, Italy is a wonder to behold. Slightly acidic water carves and erodes the soluble, sedimentary rock over many thousands of years, fracturing the terrain and creating jagged formations. Above ground is a garden of naturally-cut sculptures. Below ground lies a system of weathered caves. The place fosters a distinct feeling of oldness.

It is in this picturesque setting that a team of Italian and Australian scientists has discovered an ancient Roman highway. The etched lines of the archaic road are just tens of centimeters deep, but stand out clearly in exquisite images created with LiDAR mapping technology (see figure below).

LiDAR is carried out with a laser-firing device, often mounted onto a helicopter. For the current study, roughly four to five laser shots were fired every square meter over the survey region to measure detailed distances. When combined with geographic information system (GIS) mapping technology, the distance data allowed for the creation of a 3D map which can reveal otherwise hidden structures and formations.

The researchers decided to survey the entire region after previously discovering ancient Roman military fortifications in the area about five years ago. The highway likely connected a number of these fortifications along the Italian coast. After seeing signs of the road on LiDAR images, the research team ventured out to the region on numerous occasions to search for artifacts, especially after heavy rains, which tousled up the landscape. Willing to get their hands dirty, they were rewarded with confirmatory evidence in the form of over 200 Roman shoe hobnails found mostly along the highway, particularly those linked to caligae, heavy-soled military sandals worn by Roman soldiers. Hobnails are short nails inserted into the bottom of shoes to provide traction and increase durability.

"Hobnails discovered along the road and inside the external fortification itself could be probably linked to the presence and movements of the Roman army in the area from the period of Caesar’s Gallic War," the researchers suggest.

The hobnails, pictured in the upper left, were found at the locations marked by red dots.

Based on the types of hobnails found, the authors estimate that the road may have been in use between the 2nd century BC and the 2nd century AD, as long as 300 to 400 years! Sometime after it fell into disuse, two sinkholes opened along its path. Sinkholes are a common fixture of the limestone, karst landscape, swallowing the old to reforge something new.

The discovery was detailed in the journal PLoS ONE.

Source: Bernardini F, Vinci G, Forte E, Furlani S, Pipan M, Biolchi S, et al. (2018) Discovery of ancient Roman "highway" reveals geomorphic changes in karst environments during historic times. PLoS ONE 13(3): e0194939. https://doi.org/ 10.1371/journal.pone.0194939

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