Sundials were another early method for marking time.
The sundial, which measures the time of day by the direction of shadows cast by the sun, was widely known in ancient times.
The Sumerians used sundials. They divided the day into 12 parts and each part was about 2 hours long. They measured the length of shadows to determine how much time had passed. No one is really sure why the Sumerians kept track of time; maybe it was for religious purposes. Sundials were dependent on the weather; it would be useless on a cloudy day and the winter and summer shadows would not correspond with the markings. In order for the sundial to work correctly, it had to be positioned correctly.