Also known as Chaponost aqueduct. It was raised by Romans in order to bring water from river Gier to Lugdunum, former Lyon city. At that time, population from Lyon had increased very quickly. People needed drinking water more than anything else!
We had 4 aqueducts: first, Mont-d’Or one, wasn’t enough. So they raised Yzeron, Brévenne and Gier aqueducts. The first one dates back to the Ist century but the Gier one dates back to the 2th century, in the reign of Hadrien. A stone was found near the aqueduct, with an inscription mentioning Hadrien’s name: the famous Chagnon stone, discovered in 1887!
It’s about 160 centimetres, with a Latin sentence: Ex auctoritate imperatoris Caesaris Trajani Hadriani Augusti, nemini arandi, serendi pangendive jus est intra id spatium agri quod tutelae ductus destinatum est, which means that "emperor Caesar Trajan Hadrien Augustus forbade everyone to plant, sow or plough near the aqueduct".
Anyway, the aqueduct is the longest and most well preserved of the 4 aqueducts. Yes, we still have 75 beautiful arches (90 originally)! It was raised with a stone made of small diamonds: a special Roman way of building, pretty unusual in France: in fact, it’s the only building on our land raised with this technique...
The water started from the current city of St-Chamond, ran 85 kilometres and arrived on the Fourvière hill, in Lyon city. And we found on the aqueduct path several well preserved bridges with siphons.
What’s this? A bridge where water could run whatever the land relief, especially in hollow places like valleys. Upstream water, we have a water tank; downstream, a tank where water flows; between the two, pipes and a bridge flanked by a siphon, raises lower than the 2 tanks. So the huge pressure of the water is channel and we have no loss. At the end of the path, aqueducts ended with a kind of huge tank, very deep and vaulted.