The Basilica Cistern, also called the Yerebatan Sarayı or Yerebatan Sarnıcı, is the largest of several hundred ancient cisterns that still lie beneath the city of Istanbul.

This cathedral-sized cistern is an underground chamber of 143 by 65 metres, capable of holding 80,000 cubic metres of water. The large space is broken up by a forest of 336 marble columns each 9 metres high.

The cistern, located in the historical peninsula of Istanbul, was built by the Greeks during the reign of emperor Justinianus in the 6th century, the age of glory of Eastern Rome, also called the Byzantine Empire.