An Ancient City Nearly Vanished. The Reason Why Was Hidden in a Roman Aqueduct.

4 min readHere’s what you’ll learn when you read this story:Researchers studying carbonate deposits in a Roman aqueduct believe they discovered what caused the decline of the French city of Nîmes in early medieval times.The famed aqueduct, which features the Pont du Gard bridge, stopped sending water to the city of Nîmes during the same period when the Plague of Cyprian struck.The aqueduct deposits may tell a fresh tale of both the reach of the plague and the reason for the depopulation of Nîmes.Roughly 1,750 years ago, water stopped flowing through a famed Roman aqueduct into the French city of Nîmes. Researchers now suspect that the interruption wasn’t an engineering failure at all, but the signature of a city emptied by the Plague of Cyprian.The Roman-built aqueduct, famed for its Pont du Gard bridge, offers more than a lesson in architecture. Researchers at Johannes Gutenberg University Mainz investigated anthropogenic carbonate deposited along the aqueduct channel to “understand ancient water management strategies and environmental conditions.” What the team found, though, was a dramatic cessation of water flowing along the aqueduct to Nîmes, coinciding with an “empire-wide economic crisis and the Plague of Cyprian” around 250 to 270 C.E., according to the study the team published in the journal Geoarchaeology.While the portion of the aqueduct supplying Nîmes stopped flowing, other sections, including the Pont du Gard, remained operational for at least another 140 years. “The carbonate deposits record hydroclimate dynamics and human interference over 220-360 years during the Roman period,” the authors wrote, “and dating the breakdown of parts of the system provides insights into urban change.”Little is known about whether the Plague of Cyprian reached western Europe, but the aqueduct offers a clue that its toll may have been far greater than historians have realized.“The carbonate deposits document human interventions spanning roughly 300 years during the Pax Romana and also offer insights into social unrest,” Gül Sürmelihindi, a member of the school’s Institute of Geosciences, said in a statement.The aqueduct—built around 50 C.E.—showed evidence of three major events. The first was an expansion to include additional water sources just 11 years after its initial construction, which aligns with the timing of a well-documented dry spell in the region. A century later, the water reaching Nîmes dwindled, and the scale of the loss suggests an authorized diversion to irrigate farmland.Then came the real revelation. After about another 120 years, likely around 270 C.E., the urban water supply ceased entirely. “Nîmes was presumably depopulated by the plague,” the statement reads, “rendering the water supply to the city unnecessary.”To collect data from the 31-mile-long aqueduct, the team extracted samples of carbonate rock at 10 different locations, analyzing the layers using isotope analysis. A two-centimeter-thick carbonate layer sits at the base of each sample. Variations in water inflow and temperature cause distinct patterns to form within the layers, akin to tree rings.The first 11 years suggest drought with minimal water flow in the aqueduct, which matches documentation by Roman historian Tacitus. A new water type joined the aqueduct after 11 years, ensuring “an additional source was tapped to ensure the aqueduct had a sufficient water supply,” Cees Passchier, of the school’s Institute of Geosciences, said in a statement. At the same time, crews raised and reinforced parts of the architecture to accommodate the higher water level, and some of those changes are still visible on the Pont du Gard bridge today.The deposited carbonate layers thin out around 150 C.E., when the water level dropped. “About half of the water supplying the city was diverted to irrigate fields—given the large volume, this appears to have been an authorized withdrawal,” said Sürmelihindi.The research shows that the next 100 years offered a flawlessly functioning aqueduct. Everything changed in the mid-third century, though, when the color and composition of the carbonate switched to a more porous texture that included clay and sand—signs the aqueduct wasn’t being maintained. “Great economic and political turmoil prevailed across many parts of the Roman Empire,” said Sürmelihindi. “The carbonate deposits reveal that the city’s condition was deteriorating.”Around 270 C.E., the carbonate deposits abruptly halted near Nîmes, while estates upstream continued to use the aqueduct. “The results suggest that something happened to the population of Nîmes,” said Sürmelihindi. “It is possible that the Plague of Cyprian—which is primarily documented in North Africa and even in Rome, where it claimed many lives—also posed a problem in southern France.”The carbonate study showed that Cahors, roughly 186 miles west of Nîmes, also struggled at the same time.With the flow of water to Nîmes trickling to nil, people relied on the aqueduct for water upstream, sometimes drilling their own holes into the structure to extract water. “The city could easily have repaired the aqueduct during those 140 years,” Passchier said. “Apparently, however, the decline in population density and urban wealth was permanent.”Tim Newcomb is a journalist based in the Pacific Northwest. He covers stadiums, sneakers, gear, infrastructure, and more for a variety of publications, including Popular Mechanics. His favorite interviews have included sit-downs with Roger Federer in Switzerland, Kobe Bryant in Los Angeles, and Tinker Hatfield in Portland.