The Greeks and Romans needed a way to divide each day into segments of time. They also needed tools to help them measure the passage of time. To meet these needs, they adopted practices that the Babylonians and Egyptians had developed much earlier.

Each day began at sunrise and lasted for 24 hours—12 daylight hours and 12 darkness hours. The length of an hour, however, changed over the course of the year. In summer, when the days were longer and the nights were shorter, day and night still had 12 hours each, but the daytime hours were longer and the nighttime hours shorter. The opposite was true in winter, when days were shorter and nights were longer. This system of flexible hours remained in use for everyday purposes throughout the Greek and Roman eras. Only astronomers making precise studies of the stars bothered to measure hours of fixed length.

People told time—at least roughly—by observing the position of the sun during the day and of the moon and stars at night. An early method of telling time was a crude shadow table, using the measured length of a man’s own shadow. Shadows were longest in the early morning and late evening, while at noon they almost disappeared.

Another method of time telling involved the use of a sundial and shadows. According to the Greek historian Herodotus, the Greeks adopted the sundial from the Babylonians. By the 200s B.C., it was widely used in the Mediterranean region. The sundial consisted of a pointer that cast a shadow onto a round disk that was divided into 12 sections like the pieces of a pie.

Shadow tables and sundials were useless at night or in cloudy weather. At these times, the Greeks and Romans used a klepsydra, or water clock. The klepsydra was a vessel from which water dripped at a steady rate, measuring fixed intervals of time. If a clock held just enough water to empty itself in the 12 hours between sunset and sunrise, the user knew that 4 hours had passed when a third of the water had dripped out. The Greeks used the klepsydra to time how long a person could speak in a court of law.

The Greeks and Romans made many ingenious machines. Certainly they could have produced accurate mechanical clocks measuring fixed periods of time. It seems that they felt no need for such timepieces but were satisfied with practical, centuries-old methods of measuring time. (See also Calendars.)

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