The Basilica Cistern - Yerabatan Sarnici The Basilica Cistern, located to the west of Hagia Sophia Square in Istanbul, was constructed during the reign of Justinian I (527-565) to provide water to the nearby palaces. With a length of 140 meters and a width of 70 meters, the cistern comprises 336 columns arranged in 12 rows, each with 28 columns. These columns have various capitals, ranging from plain to Corinthian types. The level of water in the cistern varied depending on the season, and pipes were placed at different levels on the eastern wall. Originally, the cistern was used as a basilica and was named the Basilica Cistern. It is one of the largest and most magnificent covered cisterns in Istanbul. The ceiling, built entirely out of brick, is cross-vaulted, creating a forest-like effect with pillars. The cistern served many palaces of the Byzantine era and a mosque until the 17th century. During a restoration project in 1987, a meter of mud was removed, revealing the original brick pavement and two Medusa head statues. Today, visitors can walk around the cistern using the new walkway.