Yerebatan or Basilica Cistern built by the order of Emperor Constantine in 532 to supply water to city. Water was carrying outside from the city with pipe system, aqueduct and serve to city. One of the most important purposes to build that big size cistern was; to supply water to the city especially during long sieges of Constantinople. The enlarged cistern provided a water filtration system for the Great Palace of Constantinople and other buildings on the First Hill, and continued to provide water to the Topkapi Palace after the Ottoman conquest in 1453 and into modern times.
It is one of the biggest cisterns in the world with its 9,800 square meters in area and capable of holding 80,000 cubic meters of water. The ceiling is supported by a forest of 336 marble columns, each 9 meters high.
This is one of the best examples of Roman architecture. Historical texts claim that 7,000 slaves were involved in the construction of the cistern. After the restoration, it has been serving as a museum since 1987.
There are two Medusa heads in northwest corner of the cistern. Repalaced sideways and upside down. They are believed that The Romans are not pagan anymore, that’s why repalaced one of the great symbol on Antique Greek period since they become Christian after 335 when Istanbul become capital of Eastern Roman Empire.