Credited to Egypt. Where and when water clocks were first invented is not known for certain. Egypt holds the oldest physical example and the oldest written claim of invention, but water clocks were also used early in other regions.
How it began
The oldest documentation of a water clock is the tomb inscription of Amenemhet, an Egyptian court official of the 16th century BCE, which identifies him as its inventor. The oldest surviving water clock was found broken in pieces at the temple of Karnak in 1904. It is made of Egyptian alabaster and carries a scene of King Amenhotep III, which dates it to the 14th century BCE. It was used in the temple of Amen-Re at Karnak and is now in the National Museum of Egyptian Civilization in Cairo.
Before it existed
Egyptians divided the night and the day into 12 hours each and told time from the Sun or the stars. Those methods needed a clear sky. A sundial requires only sunshine and a shadow caster. The water clock was designed to be independent of weather that might hide the Sun or stars, and the scholar Anette Schomberg describes it as a step toward a device that keeps time on its own, apart from its surroundings.
How it works
The Karnak clock is shaped like a large flowerpot. Water flowed out through a very small hole in the bottom, emerging outside under the figure of a seated baboon. The sloping sides were meant to make the level fall at a nearly constant rate. Inside are 12 carved columns of 11 false holes that mark the hours of the night. There is one column for each month, because Egyptian hours varied in length with the season. To tell the time, a priest looked inside and read the water level against the nearest mark.
What changed first
Priests used these clocks to determine the time at night so that temple rites and sacrifices could be performed at the correct hour. The outside of the Karnak vessel is decorated with stars and planets in boats, the constellations of the northern sky and the gods of the twelve months, linking the instrument to the astronomical knowledge it replaced on cloudy nights.
What lasted
Until the mechanical clock appeared in the 14th century CE, sundials and water clocks were the only devices available for measuring time. Water clocks remained the most accurate timekeepers until the pendulum clock of 1656, according to Jeremy Norman's History of Information.
