This plan shows the cisterns (blue) and underground passageways (grey). The numbering system was developed by Charles Warren, who, in the 1860’s, explored many of these underground structures. Some of these underground passageways were part of Herodian gates that gave access to the Temple Mount, i.e. Cistern 30 is the underground passageway of Warren’s Gate, Cisterns 19 and 20 are part of the underground passageway of Barclay’s Gate, Cistern 1 is the underground passageway of the ancient Tadi Gate.
Some of the water cisterns, such as Cisterns 7 and 8 were enormous underground water reservoirs, capable of holding some 2 million gallons of water. Most of these cisterns were initially underground quarries from which building stones for the buildings of the Temple Mount were taken. After the quarrying activities were stopped, these caverns were plastered and became water reservoirs.