Aqueduct of the Gier

Roman Site in Lyon

CC BY-SA 2.0 / Carole Raddato

The Aqueduct of the Gier was a major feat of Roman engineering, likely constructed in the 1st century AD to supply water to Lugdunum (modern-day Lyon), then the capital of the Roman province of Gallia Lugdunensis. Sourced from the Gier River on the slopes of Mont Pilat, about 42 km southwest of Lyon, it was the longest and best-preserved of the city’s four Roman aqueducts. It served the growing city by delivering fresh water over an impressive distance and terrain.

Spanning approximately 85 km (53 miles), the aqueduct followed the natural contours of the land, weaving through various regions including Mornant, Chaponost, and Sainte-Foy-lès-Lyon. Engineers used a gentle slope of 0.1% to ensure a steady flow of water. Of the entire route, 73 km were covered ditches, some buried as deep as 4 meters, while 11 tunnels and 30 open-air sections helped the system navigate changes in elevation and geography. Access shafts were placed every 77 meters to allow for cleaning and maintenance.

The aqueduct’s most remarkable features were the inverted siphons—advanced hydraulic systems that allowed the water to cross deep river valleys such as the Garon and Trion. These siphons used pressurized lead pipes to carry water down one slope, across a high-arched bridge, and up the other side, eliminating the need for long rows of arches. The remains of these bridge piers and siphons are among the most visually striking relics of the aqueduct today and demonstrate the Romans’ mastery of both engineering and hydraulics.

While early scholars dated the construction to the 2nd century AD during Hadrian’s reign, modern evidence, including architectural styles and associated fountains in Lyon, suggest the Gier Aqueduct was likely completed around 50 AD. Built as one massive undertaking, it could only begin serving the city once fully completed—making its scale and precision even more impressive. Today, many segments of the aqueduct can still be explored, especially in places like Chaponost, offering a fascinating look into Lyon’s Roman past.

The Aqueduct of the Gier appears in our Complete Guide to Visiting Lyon!

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