Sun and water had been the standard

Sun and water had been the standard means of timekeeping until the Middle Ages. Because the twelve hours of the day were traditionally counted from sunrise to sunset, and the twelve hours of the night from sunset to sunrise, this convention led to unequal hours, hours that varied in length with the season of the year, with long daylight hours during the summer months and long nighttime hours during the winter months. Time was curiously relativistic in a sense, hours shrinking and elongating along with the seasons. But time was not an abstraction for people in the ancient world and the medieval world. It was identified with the duration of concrete processes like the irrigation of fields or the period between religious observances, duly measured in the path of the sun’s shadow or the flame’s consumption of a candle during the night—or the flow of water out of a graduated bowl.