At least 36 cisterns, excavated reservoirs, were constructed in Istanbul during Byzantine times. The largest known covered cistern is the Basilica cistern which was probably completed in the early 6th century. Figure 1 shows a plan view of the 140 × 70 m structure, which now lies partly under a road in a busy area of Istanbul. It was originally supplied by aqueduct from springs in Marmara, west of the city. Figure2 gives a general view of the interior, where the roof is supported by 336 columns.
Figure 3 shows the base of one of the column which appears to be made from a scrap sculpture of the Medusa's head. There are constant inflows of water at various points in the roof of the cistern, as can be seen from the pool of water, splashes and drips. At the time the photograph was taken in March 1988, it had not rained for at least 15 days, hence the inflow could not have been direct recharge. The water was clear and odour-free and was certainly not sewage. The probable source was leaking water mains which, without the cistern, would percolate to the water table. Thus Figure 3 provides some evidence that leaking mains recharge groundwater as argued in recent articles (Lerner 1986, 1988a, b).
My thanks to Professor Okay Eroskay of Istanbul University for help with the photography.