The Basilica Cistern, known as Cisterna Basilica in Greek and Yerebatan Sarnıcı or Yerebatan Saray in Turkish, is the largest among numerous ancient cisterns that are situated beneath the city of Istanbul in Turkey. This particular cistern, positioned 150 meters southwest of the Hagia Sophia on the historic peninsula of Sarayburnu, was constructed in the 6th century during the reign of Byzantine Emperor Justinian I. In the present day, it is maintained with minimal water to allow public access to its interior.
The name "Basilica" was given to this underground cistern due to its location beneath a vast public square known as the Stoa Basilica on the First Hill of Constantinople. Before the cistern was built, a grand basilica stood in its place. This basilica was initially constructed during the Early Roman Age between the 3rd and 4th centuries and served as a center for commerce, law, and art. It was later reconstructed by Illus following a fire in 476.
According to ancient sources, the basilica contained gardens enclosed by a colonnade that faced the Hagia Sophia. Emperor Constantine is said to have erected a structure there, which was subsequently rebuilt and expanded by Emperor Justinian after the Nika riots of 532 that ravaged the city.
Historical accounts indicate that the construction of the cistern involved around 7,000 slaves. This enlarged cistern served as a water filtration system for the Great Palace of Constantinople and other structures on the First Hill. It continued to supply water to the Topkapı Palace even after the Ottoman conquest in 1453 and up until modern times.
Over the years, knowledge of the cistern's existence faded away, except among the locals who still drew water from it. In 1565, the French traveler Petrus Gyllius left a record of his experience of rowing between the columns of the cistern and observing fish swimming in the water beneath his boat.
In terms of measurements, this cistern has the magnitude of a cathedral. It is an underground chamber that spans approximately 138 meters by 65 meters.
