In ancient times, sundials displayed the time of day, but because this method needed shadows for time telling, one would have to guess at the hour on cloudy days.
The earliest indoor timekeeping devices were water clocks and hour glasses, whose function was similar: a controlled amount of substance escaped a container, a measure of the amount released marking the passage of time.
With the advent of Christianity, calendars, prominent in monasteries, reminded the monks of Feast Days, of which there were plenty. Church bells wakened the citizens, whereupon they set out for daily tasks. Less important for peasants and commoners during the Middle Ages, timepieces were made with the nobility in mind, because workers began their day with the rising sun, and went to bed at dark.
One of the most charming, yet one of the simplest devices used, was the candle clock, which was designed to tell time at night. One of the ways a candle clock could be employed was to note the period of time it took a candle of controlled size and substance to burn to a certain length. Marks behind the candle, such as is illustrated in the picture to the right, would designate the passing hours as the candle burned.
In the early 1300s, the mechanical clock was invented in Europe, although the Arabs had used a system of gears and weights in their water clocks as early as the 11th century. During the 14th century, an escapement mechanism was devised, and two centuries later, clocks and pocket watches were spring-powered. Later, the pendulum came into use, an example of that slow, mesmerizing movement we see in longcase clocks.