Aquaeductus Gerapedus
About
The longest of Lugdunum's four aqueducts, running roughly 86 kilometers from the Gier valley and crossing the Beaunant and Chaponost valleys on dramatic inverted-siphon bridges. A 2018 tree-ring study dated the Beaunant siphon's timber foundations to 110 CE, putting the engineering work under Trajan. By 117 it had been carrying water into Lugdunum for years.
What happened here
Water arrives day and night and never stops. The channel runs mostly underground, following a shallow gradient measured out with a levelling instrument over tens of miles, and it goes up on arches only where the ground drops away. Inspection shafts sit at intervals; gangs work the line constantly, cutting out the lime crust that thickens on the walls and narrows the flow. At the town end the water is divided in a distribution tank — public fountains first by law, then baths, then private houses whose owners have paid for a pipe of a fixed and stamped size. Illegal tappings are a permanent scandal. What arrives is not stored but runs continuously, and the overflow flushes the drains.
Sources
Roman Maps shows the empire frozen at 11 August 117 CE, the day Trajan died — its moment of greatest territorial extent. Explore the full map →