The Basilica Cistern (Turkish: Yerebatan Sarayı - "Sunken Palace", or Yerebatan Sarnıcı - "Sunken Cistern"), is the largest of several hundred ancient cisterns that lie beneath the city of Istanbul (formerly Constantinople), Turkey. The cistern, located 500 feet (150 m) 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.
Istanbul (historically Byzantium and later Constantinople; see the other names of Istanbul) is the largest city of Turkey and the third largest city in the world. The city covers 27 districts of the Istanbul province.It is located on the Bosphorus Strait and encompasses the natural harbor known as the Golden Horn, in the northwest of the country. It extends both on the European (Thrace) and on the Asian (Anatolia) side of the Bosphorus, and is thereby the only metropolis in the world which is situated on two continents. In its long history, Istanbul served as the capital city of the Roman Empire (330–395), the East Roman (Byzantine) Empire (395–1204 and 1261–1453), the Latin Empire (1204–1261), and the Ottoman Empire (1453–1922). The city was chosen as joint European Capital of Culture for 2010. The historic areas of Istanbul were added to the UNESCO World Heritage List in 1985.