The Barbegal aqueduct and mills is a Roman watermill complex located on the territory of the commune of Fontvieille, 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 sixteen overshot wheels are considered the biggest ancient mill complex.
The Barbegal mills are located 12 kilometers north of Arles near Fontvieille, where the Arles aqueduct arrived at a steep hill. The mills consisted of 16 waterwheels in two parallel sets of eight descending a steep hillside. There are substantial masonry remains of the water channels and foundations of the individual mills, together with a staircase rising up the hill upon which the mills are built. The mills operated from the beginning of the 2nd century until about the end of the 3rd century. The capacity of the mills has been estimated at 4.5 tons of flour per day, enough to supply bread for as many as 10,000 of perhaps 30-40,000 inhabitants of Arelate at that time. It is thought that the wheels were overshot water wheels with the outflows driving successive wheels to the base of the hill.
The Roman aqueducts that fed the mills were also built to supply water to the town of Arles (then called Arelate). The two aqueducts joined just north of the mill complex and a sluice controlled the water supply to the complex.
Vertical water mills were well known to the Romans, being described by Vitruvius in his De architectura of 25 BC, and mentioned by Pliny the Elder in his Naturalis Historiæ of 77 AD. There are also later references to floating water mills from Byzantium and to sawmills on the river Moselle by the poet Ausonius. The use of multiple stacked sequences of reverse overshot water-wheels was widespread in Roman mines, especially in Spain and Wales. It is possible that the mills at Barbegal may also have been used for sawing timber and stone when not grinding wheat. The Hierapolis sawmill from the 3rd century AD shows a crank-activated frame saw being used in this way, and another has been excavated at Ephesus.
Visitors to Barbegal may park where a minor road crosses the massive remains of the original aqueduct, and walk south about 250 meters along the remains of the aqueduct through the cleft in the ridge to the top of the mill complex. The site is signposted as Roman aqueduct rather than as a mill. The Arles Museum of Antiquity has an informative reconstructed model of the mill. The site is currently overgrown, and care is needed exploring the ruins.
The English science historian James Burke examines Roman watermill technology such as that of the Barbegal aqueduct and mill, concluding that it influenced the Cistercians and their waterpower, which in turn influenced the Industrial Revolution, in the fourth of his ten-part Connections, called "Faith in Numbers".