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

This cathedral-sized cistern is an underground chamber of 140 by 70 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.

At the far end of the Cistern, there are two heads of Medusa which are put upside down or horizontal. The Medusa Heads are taken from an ancient Pagan site but they complement the pillars very beautifully and add a different taste to the building.

The cistern was built by Emperor Constantinus I during the 4th century and was restored and extended by Justinianus in the 6th century. The water came from the Belgrad forest via the Cebecikoy arch.

It was used as a location for the James Bond film From Russia With Love.

It was restored in 1980's and today walkways have been constructed right through the cistern and subdued illumination gives the place a suitably mysterious athmosphere.