Researchers from Johannes Gutenberg University Mainz (JGU) have studied carbonate deposits in the Roman aqueduct near Nîmes, France, to learn more about ancient water management and possible historical events. The aqueduct, built around 50 A.D., was expanded after 11 years of operation to include an additional water source. This expansion coincided with a documented dry period in the region. A century after its construction, the city's water supply was deliberately reduced, likely to divert water to nearby farmland. About 120 years later, the aqueduct stopped supplying water to the city entirely, around the time of an empire-wide economic crisis and the Plague of Cyprian (250–270 A.D.). Nîmes may have been severely affected by the plague, leading to its depopulation and the end of the need for urban water supply. The team, led by Professor Cees Passchier and Dr. Gül Sürmelihindi from JGU's Institute of Geosciences, collected carbonate rock samples from 10 locations along the 50-kilometer aqueduct. Using isotope analysis, they found distinct patterns in the rock layers, similar to tree rings, that reflect changes in water flow and temperature over time. At the base of the samples, a two-centimeter-thick carbonate layer covered by a thin clay layer suggests a drought in the western Mediterranean, an event also noted by the Roman historian Tacitus. After 11 years, a different type of water was introduced, indicating an additional source was used to maintain the aqueduct's supply. Today, structural modifications, such as raised and reinforced walls, can still be seen on the Pont du Gard bridge. Around 150 A.D., carbonate layers became much thinner, signaling a drop in water levels. About half of the city's water was diverted to irrigate nearby fields, a move likely approved by influential individuals. The aqueduct continued to operate with reduced water flow for about 100 years. By the mid-third century, the carbonate layers changed in color and composition, becoming more porous and containing clay and sand—signs of declining maintenance. Around 270 A.D., carbonate deposits stopped entirely in samples near the city, indicating the water supply to Nîmes was completely cut off. Instead, owners of large estates upstream began using the aqueduct for their own needs, as shown by continued carbonate deposits in rural sections of the aqueduct. The study suggests that the Plague of Cyprian, which is well-documented in North Africa and Rome, may have also impacted southern France. Archaeological findings support the idea that many cities in the region, including Cahors, faced crises around this time, some due to invasions by barbarian groups and others for unknown reasons. In rural areas, water from the aqueduct continued to be used for agriculture for another 140 years, into the fifth century. People drilled holes into the aqueduct's walls to access water, leaving massive limescale deposits on the structure. However, the decline in population and urban wealth appears to have been permanent.