Water Clocks

Waterclocks, like sundials, may have been used as long ago as 4000 B.C. Through the centuries, water clocks became more sophisticated, with gears and revolutionary mechanisms. Water clocks would finally be replaced in the 18th century with pendulum clocks.
The oldest water clock documentation is on the tomb of a 16th century Egyptian court official, Amenemhet. He is portrayed as the inventor, though it is possible he only made improvements on an earlier model.
The earliest clocks were stone vessels with sloping sides that allowed water to drip at a nearly constant rate from a hole near the bottom. Marks inside the bowl measure the passing of time as the water level lowered in the vessel.
Clocks were used by priests, to time the correct “hour” for rites and sacrifices. The clocks were also possibly used during the day, especially by the wealthy.
The image is of two waterclocks from the Ancient Agora Museum in Athens. The top vessel is an original from the 5th c. B.C. The lower vessel is a reconstruction of a clay original.