In the 1920s, Jesuit priest Antoine Poidebard spotted the angular outlines of what he suspected were ancient Roman forts while flying over the Syrian desert in a biplane. In what was one of the earliest aerial archaeological surveys, the French aviator went on to map and photograph more than 100 outposts strung along a 1000-kilometer arc between the Tigris and Euphrates rivers.
For decades, historians assumed these were the remains of a defensive frontier built around 300 C.E. to fend off the Sasanian Empire, Rome’s rival to the east. Now, archaeologists are suggesting a more mercantile explanation, thanks to the discovery of hundreds of additional Roman-style structures seen in declassified U.S. spy satellite photos. Rather than a linear defensive screen like Hadrian’s Wall in northern England and others the Romans erected, the Syrian forts were probably there to protect and tax caravans and traders, not to constantly fight the Sasanians, the researchers report today in Antiquity.
“If confirmed, this adds a lot to the discussion,” says Rocco Palermo, an archaeologist at Bryn Mawr College who was not involved in the work. “By adding more forts, the scenario really changes.”
To identify the forts, Dartmouth College archaeologist Jesse Casana and colleagues consulted photos taken from low-orbit satellites at the height of the Cold War. Classified under codenames such as CORONA and HEXAGON, the images were released to the public in the 1990s. Because the photos predate industrialized agriculture, they capture features in the landscape that have since been disturbed or destroyed by mechanized plows. Sharp-eyed scholars have in the past used the images to identify ancient humanmade features in the landscape, including ruined cities, road networks, and rounded mounds known as “tells” left by mud brick buildings.
Casana usually excavates Mesopotamian sites in northern Iraq, often using CORONA and other declassified satellite images to find ruins. But with fieldwork on hold during the COVID-19 pandemic, he and his team turned their attention to black-and-white images of an adjacent region: the sprawling 300,000-square-kilometer Syrian plateau. Dividing the area into 5-kilometer squares, they hunted for signatures of humanmade structures that stood out against the dry desert backdrop.
The team identified more than 4500 such features, including 396 square or rectangular structures resembling Roman-style fortifications. “When you find something Roman, you know it. It’s big, and square, and stone,” Casana says. “One of the things that became apparent was there were a lot more square things out there than we realized.”
Because Poidebard only flew over a small part of the region, he never saw most of these features. “He believed they would be along the border, so he flew his plane along the border and found a bunch of forts,” Casana says. Poidebard’s interpretation—that the forts were a desert version of fortified walls like those the Romans built in Europe—informed decades of historical and archaeological work in the region.
The spy satellite images, however, showed something different. Rather than a single line of small forts running north to south, the newer photos revealed hundreds more running east to west. “We can see Poidebard’s distribution was false,” Casana says. “In reality, there’s a huge number that extend from the eastern Mediterranean to the Tigris River.”
The locations parallel likely trade routes that once connected Roman ports along the Mediterranean Sea to Silk Road trade routes. These small, scattered forts could have protected traders from bandits or lions, but they would have offered little resistance against an invading army, Casana says.
Palermo agrees with that interpretation. “Rather than defensive strongholds, they were like gas stations, where people stopped for food and a roof over their head for a night,” he says. “Soldiers were stationed there to protect Rome’s business goals.”
That would support a growing consensus that the Syrian desert was different from Rome’s other border zones, Palermo adds. Hadrian’s Wall or the Rhine River represented stable, militarized frontiers, but in Syria, the Romans and Sasanians may have competed for influence among local tribes and kingdoms. “It was a huge buffer area,” Palermo says. “For the first time, someone’s using satellite imagery to confirm what historians suspected, or see new patterns on this fluctuating frontier.”
Ordinarily, the next step would be to excavate some of the sites to see whether archaeological evidence matched that interpretation. Precise dates might show that some suspected forts were caravan stops built by later kingdoms or empires, for example. “Roman civilization brought a lot of innovations, but they didn’t invent the square,” says Jason Ur, a Harvard University archaeologist not involved with the work. “It would be very premature to come to social interpretations without groundwork to date the sites.”
War, however, has made the survey area—which runs along the modern border between Syria and Turkey—too dangerous for in-person archaeology. “I’m skeptical without groundtruthing we can push this topic much further. We need to put shovels in the ground,” Palermo says. “But this is an important stepping stone for future research, once things get stable in the region.”
