Byzantine cistern from the 6th century built by Justinian I and is located to the south-west of Hagia Sophia. The water was brought from Belgrade Forest, 19 kilometers to the north of Istanbul, and it had a capacity to store 100.000 tons of water. It features fine brick vaulting supported by 336 various type of columns brought here from different parts of the Empire. The Basilica Cistern, or Underground (Yerebatan) Cistern as locals call it, now houses a cafeteria and hosts musical and theatrical performances and a Biannual. There are also two Medusa friezes brought from the Temple of Apollo in Didyma (today's Didim).