Drawing of the Barbegal mill complex Cees Passchier, Mainz, Germany

It was once thought that watermills only began to be used on an industrial scale in medieval times. But in 1937 a Roman complex with 16 water wheels was found in Barbegal in southern France – the largest ancient water-powered factory found anywhere in the world.

Now it has been shown that the Barbegal factory probably specialised in producing flour for making ship biscuits, rather than for supplying the nearby Roman city of Arelate as previously assumed.

During excavations of the site in 1937 archaeologists discovered thick limescale deposits that had …