An informal article that looks at the evolution of time measurement and the development of clocks describes three early Egytian time keeping devices - sundials, merkhets and water clocks. See the above article for the full story, but here's a sample: "Water clocks were among the earliest timekeepers that did not depend on the observation of celestial bodies. One of the oldest of this type was found in the tomb of Amenhotep - I, buried around 1500 B.C. These were stone vessels with sloping sides that allowed water to drip at a nearly constant rate from a small hole near the bottom. Markings on the inside surface measured the passage of time as the water level reached them."