Basica Cistern

The Basilica Cistern, "Subterranean Cistern" is the largest of several hundred ancient cisterns that lie beneath the city. It got its name due to the proximity to the basilica.

This cathedral-sized cistern is an underground chamber approximately 138 metres  by 65 meter, about 9,800 m2. It is capable of holding 80,000 m3 of water. The ceiling is supported by a forest of 336  marble columns, each 9 m tall.