Barbegal Aqueduct

The Barbegal aqueduct and mills was a Roman watermill complex located on the territory of the commune of Fontvieille, Bouches-du-Rhône, near the town of Arles, in southern France. The complex has been referred to as "the greatest known concentration of mechanical power in the ancient world" and the 16 overshot wheels are considered to be the largest ancient mill complex.Another similar mill complex existed on the Janiculum in Rome, and there are suggestions that further such complexes existed at other major Roman sites, such as Amida.

Source: Wikipedia