Before watches and modern clocks, the ancient Romans used clepsydras, or water clocks, to measure the passage of time. This device worked by passing water from one container to another, usually through a small hole. As the water level fell (or rose), marked scales showed how much time had passed.
Their use was written about by, among others, Vitruvius, a Roman architect and engineer, who described the different types of water clocks used in Rome in his work De Architectura (IX.8). Pliny the Elder, in Natural History (VII.60), also mentions the use of clepsydras.
