An industrial machine powered by gravity
Near the Roman city of Arelate, modern-day Arles, engineers in the 2nd century AD built a massive flour mill complex into a steep hillside. The Barbegal mills are considered the greatest known concentration of mechanical power in the ancient world. The design harnessed gravity. Two Roman aqueducts converged just north of the site, funneling water into a channel that split to feed the mill. A sluice gate allowed operators to control the flow, directing water down a steep incline.
The complex consisted of two parallel rows of eight waterwheels each. The water was channeled to the top of the first wheel in a design known as an "overshot" wheel. This method is more efficient than an undershot wheel (where the water pushes the bottom), as the weight of the water falling into buckets on the wheel's rim provides most of the turning force. The water from the first wheel then flowed out and was directed onto the wheel below it, creating a cascade of power that continued for all eight wheels in the series. This sequence repeated in a parallel set of eight more wheels. The substantial masonry remains of the water channels and the foundations for each individual mill are still visible today, alongside a central staircase.