The Basilica Cistern, or Cisterna Basilica, is the largest of several hundred ancient cisterns that lie beneath the city of Istanbul, Turkey. The cistern, located 150 metres (490 ft) southwest of the Hagia Sophia on the historical peninsula of Sarayburnu, was built in the 6th century during the reign of Byzantine emperor Justinian I. Today it is kept with little water, for public access inside the space.
Basilica Cistern
The second Medusa head pillar
Unique "peacock-eyed" column in the Basilica Cistern
A cistern is a space excavated in bedrock or soil designed for catching and storing water. To prevent leakage, the interior of the cistern was often lined with hydraulic plaster.
Portuguese cistern (Mazagan), El Jadida, Morocco (1514)
The difference between a cistern and a well is in the source of the water: a cistern collects rainwater where a well draws from groundwater.
Ancient Buddhist rock-hewn cistern at Pavurallakonda in India
One of the Cisterns of La Malga, Carthage, 1930