In the Roman Empire water-powered mills were described by Vitruvius by the first century BC. The Barbegal mill had sixteen water wheels processing up to 28 tons of grain per day. Roman waterwheels were also used for sawing marble such as the Hierapolis sawmill of the late 3rd century AD. Such sawmills had a waterwheel which drove two crank-and-connecting rods to power two saws. It also appears in two 6th century Eastern Roman saw mills excavated at Ephesus and Gerasa respectively. The crank and connecting rod mechanism of these Roman watermills converted the rotary motion of the waterwheel into the linear movement of the saw blades.