Byzantine cistern from the 6th century built by Justinian I and is located to the south-west of Hagia Sophia. The water was brought from Belgrade Forest, 19 kilometers to the north of Istanbul, and it had a capacity to store 100.000 tons of water. It features fine brick vaulting supported by 336 various type of columns brought here from different parts of the Empire. The Basilica Cistern, or Underground (Yerebatan) Cistern as locals call it, now houses a cafeteria and hosts musical and theatrical performances and a Biannual. There are also two Medusa friezes brought from the Temple of Apollo in Didyma (today's Didim). Its dimensions are 140x70x9 meters.

Basilic - Yerebatan Cistern was built in the left side of Sultanahmet Square towards St. Sophia - Gulhane Park direction. Basilic - Yerebatan Cistern which is also called “Yerebatan Palace” was commissioned in about 540 by Byzantine Emperor Justinianus the 1st. The area which was gained by the underground carving of a rocky surface, the cistern which is supported by more than 300 columns, have become the most important water resource supplying water to Istanbul.

The Basilic - Yerebatan Cistern which was cleansed and repaired by the Municipality of Istanbul between 1985-1988, is today one of the open-to-public places of visit with its mystifying and exotic atmosphere.