The Romans were accomplished hydraulic engineers and built impressive water delivery systems to supply their cities with good water. An aqueduct from the Alpilles mountains brought water to Arelate, a distance of about 25 km. At modern-day Barbegal, 12 km to the north of Arles, the water dropped precipitously. The Romans used the flow to power water wheels. There were two parallel sets of eight large water wheels in stacked sequences. Flow from each wheel turned the wheel below, maximizing the energy generated by the falling water. The wheels in turn drove mills for grinding flour and saws for cutting lumber and stone. There were many such industrial sites throughout the Roman Empire, but Barbegal was one of the largest.