The Barbegal aqueduct and mills is a Roman watermill complex located on the territory of the commune of Fontvieille 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 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.
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.
References:The Walls of Constantinople are a series of defensive stone walls that have surrounded and protected the city of Constantinople (today Istanbul) since its founding as the new capital of the Roman Empire by Constantine the Great. With numerous additions and modifications during their history, they were the last great fortification system of antiquity, and one of the most complex and elaborate systems ever built. They were also the largest and strongest fortification in both the ancient and medieval world.
Initially built by Constantine the Great, the walls surrounded the new city on all sides, protecting it against attack from both sea and land. As the city grew, the famous double line of the Theodosian Walls was built in the 5th century. Although the other sections of the walls were less elaborate, they were, when well-manned, almost impregnable for any medieval besieger.