It was not easy for the Romans to keep a close track on time. They were not, as we are, inveterate clock-watchers. They did not work by minutes, let alone seconds, their smallest unit being the hour. Even that was not standardised, but varied according to season and location. By day, a Roman hour was a 12th of the time between sunrise and sunset, and by night a 12th of the time between sunset and sunrise. The length of this hour therefore depended on the time of year and on how far north or south you were.
Other than estimating from the position of the sun in the sky or by the length of shadows, the Romans had two ways of telling the time. One was the sundial – which was not much use in cloudy weather and even less by night. The other was the water-clock or clepsydra – in its simplest form a bowl of water with a small hole at the bottom which emptied in a given time.
The simple water-clock was fine for measuring, say, the period allocated for a speech in the law-courts. But it did not empty at a constant rate: the fuller it was – the greater the head of water – the faster the outflow, and the emptier, the slower. Moreover, short of a hit-and-miss adjustment of the size of the hole with wax, it could not cater for seasonal hours. One Roman remarked that it was easier to find agreement between philosophers than between clocks!
