The Basilica Cistern. This underground structure acquired its name from a large public square called Stoa Basilisca that was located in the first hill in Constantinople, which was constructed originally underground before it was converted into a cistern. It was getween the third and the fourth century during the early Roman age as a commercial, legal, and artistic centre. The Basilica was reconstructed after the fire of 476. The ancient texts indicated that the Basilica has contained gardens surrounded by pillars, facing Hagia Sophia. According to ancient historians, Emperor Constantine has built the structure, which was rebuilt later on and enlarged by Emperor Justinian after the riots in Nika in 532 which destroyed the city. That ground cistern had a water filtiration system dedicated to the Great Palace of Constantipole and other buildings located on the first hill. It continued providing water to the Topkapi Palace after the Ottoman age in 1453 up to the modern age.