The first timepieces were water clocks which had major problems with leakage, evaporation and mineral deposits from hard water. It wasn't until early in the 14th century that the mechanical escapement was developed allowing clocks to be regulated by process other than the flow of water (say by a weight falling). In 1583 Galileo observed the regular motion of a pendulum (in his case an altar lamp) and developed the first pendulum clock. The use of pendulums allowed clocks to be accurate to within 10 seconds per day as opposed to 15 minutes per day.
Many early clocks signaled (via sound) the passing of an hour or particular time (say, when monks need to rise and perform their monastic duties). It was only later that hands were added and even then it was normal for a clock to have only one hand indicating the current hour.
- Plans for a wooden wheel clock using a mechanism very similar to 16th century Swiss designs- http://www.woodenclocks.co.uk/Clock4.pdf
- A Brief History of Precision Timekeeping - http://www.ozdoba.net/swisswatch/history_part1.html
- Title: Clockwork Universe: German Clocks and Automata, 1550-1650