A Roman hillside of sixteen waterwheels fed an entire town
In the second century AD, at Barbegal in southern France, sixteen overshot waterwheels stepped down a slope, each turning its own flour mill. Together they could grind an estimated 4.5 tonnes of flour a day, enough bread for the 12,500 people of nearby Arelate. No other ancient site is known to have packed so much machine power into one place.
Waterpower is older than Rome. The Greek engineer Philo of Byzantium described a water-driven wheel in the third century BC, and the historian M.J.T. Lewis argues that those passages, once dismissed as later Arabic additions, belong to the original text. Lewis places the horizontal-wheeled mill in Byzantium in the first half of that century and the geared vertical-wheeled mill in Ptolemaic Alexandria around 240 BC. The Greek poet Antipater of Thessalonica, writing around the turn of the era, celebrated a mill that let the women who ground grain by hand sleep past dawn while water nymphs did their work.
Two designs dominated. Greek mills used a horizontal wheel on a vertical shaft, simple but needing fast water and small millstones. Roman mills set a vertical wheel on a horizontal shaft and required gears to redirect the power, and the engineer Vitruvius gave the first technical description of one between 40 and 10 BC. Vertical wheels are further sorted by where the water strikes the paddles: undershot, overshot or breastshot.
Grinding grain was only the start. Pliny recorded water-powered trip hammers across much of Italy around 70 AD, and a fulling mill for cloth existed at Antioch by 73 or 74 AD. A third-century stone sawmill at Hierapolis is the earliest known machine with a crank and connecting rod, and the earliest turbine mill turned up in Roman North Africa. Only a few dozen Roman mills have been found, but the spread of aqueducts suggests many more await discovery.
Mills could even float. When the Goths besieging Rome in 537 cut the aqueducts feeding its mills, the general Belisarius moored boats in the fast-flowing river and fitted them with wheels. Mills also reshape rivers: their channels silt up and nearby floodplains flood more often, while removing them lets streams cut deeper.
Source: Watermill
