Built by Emperor Justinianus in 532, the Basilica Cistern is also known as the Basilica Cistern because it is located under the Stoa Basilica. The cistern is a giant structure that covers a rectangular area of 140 meters in length and 70 meters in width. There are 336 columns, each 9 meters high, inside the cistern, which can be accessed via a 52-step stone staircase. These columns, erected at intervals of 4.80 meters from each other, form 12 rows, 28 in each row.
These columns rising out of the water remind of a vast forest and impress the visitor as soon as they enter the cistern. The ceiling weight of the cistern was transferred to the columns through cross-shaped vaults and round arches. Most of the columns, most of which were apparently collected from older buildings and carved from granite of various types of marble, consist of a single piece, and some of them consist of two pieces on top of each other. The titles of these columns have different characteristics from place to place. While 98 of them reflect the Corinthian style, some of them reflect the Doric style. The brick-built, 4.80-meter-thick walls and brick-paved floor of the cistern were plastered with a thick layer of Khorasan mortar, making it waterproof. This cistern, which has a total area of 9 thousand 800 square meters, has a water storage capacity of approximately 100 thousand tons.
The water of the cistern, in which 7 thousand slaves worked, was brought from the Eğrikapı water distribution center in the Belgrade forests, 19 kilometers away from the city, with the help of the 971-meter-long Valens (Bozdoğan) aqueduct built by Emperor Valens in (368) and the 115.45-meter-long Mağlova Aqueduct built by Emperor Justinian. The majority of the columns in the cistern are cylindrical, except for a few that are angular or grooved. Among these columns, the one decorated with the repetition of Peacock Eye, Drooping Branch and Tear shapes in carved and relief form attracts particular attention. This column is from IV. It is similar to the columns in the triumphal arch of the great Theodesius (379-395) from the 16th century.
The two Medusa heads used as pedestals under the two columns in the northwest corner of the cistern are masterpieces of Roman Age sculpture art. Those who visit the cistern watch in amazement IV. Although there is no exact information about which building these heads from the 16th century were taken here from, it is thought that they were removed from an ancient building from the Young Roman Period and brought here.
After the conquest of Istanbul by the Ottomans in 1453, the Basilica Cistern was used for a while and water was supplied to the gardens of Topkapı Palace, where the sultans lived. The cistern, which was apparently not used by the Ottomans, who preferred tap water, that is, flowing water, rather than still water, after establishing their own water facilities in the city, was rediscovered by the Dutch traveler P. Gyllius, who came to Istanbul in 1544-1550 to investigate Byzantine ruins.