The Pont du Gard viaduct was built by the Romans about 19 BC to bring water from the springs at Uzes to Nimes, sometimes through underground channels dug out of solid rock. Slaves used pulleys and wheels to haul the 6 ton stones into place. And there was no mortar used.
Projecting stones were built into the design to hold scaffolding.
Visitors can walk across the bottom bridge of the three tiers to the other side of the river Gardon.