Ancient Chinese astronomers used water clocks, which kept time by dripping water into a container at a constant rate.
The limitations of water clocks had long been recognized in northern Europe: among other difficulties the water usually froze in winter.
While never reaching the level of accuracy based on today's standards of timekeeping, the water clock was the most accurate and commonly used timekeeping device for millennia.
Many historians believe that the building contained a water clock that was hydraulically powered with water flowing down the steep Acropolis hill.
A watch of two or three men on the deck looked after the trimming of the sails and called out the hours by the water-clock.
