Use of water power to mill grain never ended, but the Romans were remarkable in use of machinery to accomplish work. One of the Roman mines in Spain used water power (via an aqueduct of some miles length) to "pan" for the gold at a high rate of speed.
I couldn't find a picture, but I've seen the remains of what was believed to be a Roman water-powered saw that cut slabs of marble or limestone. They were so darned...competent. I think that is what fascinates me about them, on one hand they seem modern in so many ways (roads, aqueducts, water-powered mills), but on the other hand they're so retro with their superstitions and entrail interpreting.