Glanum
About
Roman engineers built this dam in the 1st century BCE across the Vallon de la Baume gorge just south of Glanum to store water for the growing Gallo-Greek town below, making it the earliest known arch dam anywhere in the ancient world. Standing 12 meters high and 18 meters long, it curved against the water pressure the way modern arch dams still do, a principle later Roman engineers in Spain and North Africa would reuse for centuries. Glanum had grown up around a sacred healing spring, and this dam let the town keep both its ritual pool and its everyday water supply flowing through dry Provençal summers. The dam survived close to two thousand years before a modern replacement destroyed its remains in 1891.
What happened here
Built to hold water for a town, a farm or a mine, and shaped by what the local rock allows: a straight wall of masonry backed with earth, or a curved one where the gorge is narrow. The core is concrete and rubble, faced in cut stone, and the upstream face is often waterproofed with mortar. Water is drawn from a tower with sluices at different heights, so the supply keeps running as the level drops and the silt stays at the bottom. Overflow channels carry the winter flood past the wall rather than over it — the detail that decides whether a dam survives. Silt is the long enemy; a reservoir has a working life and everybody involved knows it.
Sources
Nearby
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