The 1001 Columns Cistern, also called the ‘Philoxenus Cistern’ or ‘Binbirdirek Cistern’ in Turkish, is the oldest known cistern in Istanbul.

Constructed under a palace, often identified as the Palace of Antiochos in the 5th century, this cistern is a massive reservoir that is surrounded with a thick wall all around. Inside the cistern there were 224 columns (16 rows x14 columns) with the dimensions of 64m, 56m, 40m. Today, you can see only 212 of them exist. The gap between the two columns is 3.75m and the columns are connected to each other with arches which carry the transversal vaults. - See more at: http://www.binbirdirek.com/History#sthash.wv7fDfe6.dpuf