This cistern is thought to have been built after the Nika revolt in 532 AD. It was known as the Basilica Cistern during the Roman period, as there was a Stoa Basilica above the pre-existing one at the time. After the conquest of the city by the Ottoman Turks, it was forgotten of and nobody knew that it existed. Re-discovered in 1545, it was used to water the gardens of Topkapi Palace. Restored in 1987, it has a rather eery and mystical ambiance.