Alternations

In the 3rd c BCE two supplementary tanks were added to the water clock in the Agora, set at
different levels, which were filled gradually. The time was no longer estimated by emptying the
main tank but by the gradual filling of one supplementary tank. At the end of the day the main
tank would be emptied through a large outlet hole set at its bottom. With this system all the
problems caused by water pressure changes would be avoided. This water installation was
dismantled in the 2nd c BCE. It is the forerunner of the water clock in the Tower of the Winds,
the clock of the astronomer Andronikos Kyrrestes.