Natural History (Pliny) - Watermills

Watermills

The same book describes how the grain is ground using pestles powered by water wheels, an important reference to a practice supported by the remains of many Roman water mills found across the Empire. The most impressive extant mills are found at Barbegal in southern France, using water supplied by the aqueduct supplying Arles. The water powered no less than sixteen overshot water wheels arranged in two parallel sets of eight down the hillside. It is thought that the wheels were overshot water wheels with the outflow from the top driving the next one down in the set, and so on 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.

A sawmill powered by a water wheel is known from another bas-relief from Hierapolis. Rather than using the direct drive from the rotating shaft, the Hierapolis sawmill powered a crankshaft to activate the long saw blades in cutting stone. Part of the apparatus on the sarcophagus shows a gear train, so the speed of cutting could be increased or even controlled by appropriate choice of the gearing. Some partly cut stones have also been found at the site, confirming the method. The same technique could also have been used to cut timber.

There are later references to floating water mills from Byzantium. The Aqua Traiana fed water mills arranged in a parallel sequence at the Janiculum, under the present American Academy in Rome. The milling complex had a long history and were famously put out of action by the Ostrogoths when they cut the aqueduct in 537 AD during the first siege of Rome. Belisarius restored the supply of grain by using mills floating in the Tiber. The complex of mills bear parallels with a similar complex at Barbegal in southern Gaul 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.