The Pont du Gard, a three-tiered Roman aqueduct bridge spanning the Gardon River, is one of the most famous remnants of a vast aqueduct system that once carried water for nearly 50 kilometers between the towns of Uzès and Nîmes. This aqueduct, which operated for about 150 years before gradually falling into disrepair, featured a complex design with 15 kilometers of ground-level channels, six kilometers of elevated sections, and 35 kilometers of underground or buried passages, including four kilometers of tunnels. The waterway inside the aqueduct, called the specus, was 1.20 meters wide and 1.80 meters high, with a vaulted ceiling most of the time. The walls were made watertight using a layer of tile concrete, covered in red paint that had a practical function beyond decoration—it helped maintenance workers know when to stop cleaning mineral deposits from the walls. The aqueduct began at a fountain near Uzès, called the fontaine de l’Eure, and stretched about 50 kilometers to Nîmes, even though the straight-line distance between the two cities was only about 20 kilometers. The longer route was chosen to avoid digging through limestone hills, which would have been costly and difficult. Over time, water containing dissolved limestone left visible deposits on the walls of the aqueduct. Beyond the Bornègre bridge, heading toward the Pont du Gard and Nîmes, these deposits have grown so thick—ranging from a few millimeters to 50 centimeters—that they have hidden the original canal. These layers of mineral buildup, known as carbonate deposits, provide a kind of geological record of the aqueduct’s history. Studies of these deposits reveal two main periods of operation. The first, lasting about 150 years, was marked by clear water, indicating normal function. The second, beginning in the middle of the third century, shows signs of erosion and sediment, suggesting the structure was deteriorating. The red paint on the walls was not just decorative—it acted as a marker for maintenance workers, telling them when to stop removing buildup from the walls. The aqueduct, constructed between 40 and 80 AD, likely under Emperor Claudius, eventually fell into decline as Roman maintenance efforts in the region waned. Without regular repairs, cracks expanded, deposits narrowed the water flow, and water eventually found new paths. During the Middle Ages, many stones from the aqueduct were repurposed for local buildings, such as the church of Saint-Bonnet-du-Gard. However, the massive Pont du Gard could not be dismantled easily, so it remained standing. After the aqueduct stopped carrying water, the bridge was converted into a road bridge, allowing it to continue serving the region. Today, thirteen communes in the Gard department preserve pieces of the aqueduct’s buried network, though most of these remnants are hidden beneath the landscape or incorporated into dry stone walls.