His book would have been of assistance to Frontinus, a general who was appointed in the late 1st century AD to administer the many aqueducts of Rome. Frontinus wrote De aquaeductu, the definitive treatise on 1st-century Roman aqueducts, and discovered a discrepancy between the intake and supply of water caused by illegal pipes inserted into the channels to divert the water. The Roman Empire went far in exploiting water power, as the set of no fewer than 16 water mills at Barbegal in France demonstrates.