Visit the Basilica Cistern, built in the 4th century and enlarged in 532 AD, used as water storage during Byzantine times. Listen to your guide as they explain the mystery of Medusa heads from Greek mythology. Explore this cathedral-size cistern, built during the reign of Emperor Justinian I in 532 A.D. to supply water to the Great Palace. It stores up to 80,000 cubic meters of water, delivered via 20 kilometers of aqueducts from a reservoir near the Black Sea. Descend the fifty-two stone steps into the entrance of the cistern. The cistern is surrounded by a firebrick wall with a thickness of 4 meters, coated with a waterproofing mortar. Hear how the Basilica Cistern's water comes from the Eğrikapı Water Distribution Center in the Belgrade Forest and travels through the 971-meter-long Valens Aqueduct and the 115-meter-long Mağlova Aqueduct, built by the Emperor Justinian.