Water clock

This monumental water clock was constructed at the end of the 4th c BCE in a prominent location
at the southwest corner of the Agora square, on the street leading from the Agora up to the Pnyx.
Water was drawn by a stone conduit. The device was at first a simple outflow clock, a stone tank
or cistern accessible through a flight of steps, with a small bronze outlet hole at the bottom which
allowed the tank to drain slowly. Some flotation device would record the passing hours as the
water level fell. The full tank would take some 17 hours to empty. The plug would be pulled at
dawn each day.