|This article is about the location. You may be looking for the memory.|
The cistern, located 150 meters southwest of the Hagia Sophia, was originally a basilica. During the reign of the Byzantine Emperor Justinian I, it was converted into a water storage facility for the palace complex situated immediately to the east. Following the fall of the Latin dynasty and the restoration of the Palaiologi, the cistern fell out of use and was forgotten about by by all but a few residents of the city.
Niccolò Polo had the first of the Assassin Altaïr Ibn-La'Ahad's Masyaf Keys hidden in the Yerebatan Cistern in 1257. In 1511, Ezio Auditore da Firenze, Mentor of the Italian Assassins, entered the cistern via a secret passage in the old Polo trading post, then a bookshop run by Sofia Sartor.
There, Ezio found that the Byzantine Templars had been searching for the Key for thirteen months, without success. Stealthily making his way through the Yerebatan Cistern, Ezio recovered the Key, as well as a map to the location of the other keys.
By this point, the cistern's existence had become unknown to Constantinople's general populace, though rumors persisted. It was rediscovered late into Suleiman I's reign by a visiting diplomat, who relayed his findings to the Sultan.
- Yerebatan is a Turkish word meaning "sunken", and the place is also known as Yerebatan Sarayı ("Sunken Palace") and Yerebatan Sarnıcı ("Sunken Cistern").