http://www.ottomanmosques.net - The Basilica Cistern (Yerbatan Sarn?ç in Turkish) is located in Sultanahmet district of Istanbul. It is one of the most important touristic attractions of the city. The Cistern was built in the 6th century across the Haia Sophia. The Cistern provided water to the buildings during the Byzantine and the Ottoman periods. This underground place is composed of 336 marbles columns.