The Cistern of Aspar (κινστέρνα του Άσπαρος) was a huge open-air water reservoir located on the Fifth Hill of Constantinople. It is now next to the Mosque of Sultan Selim. The cistern was built by the Patrician Aspar in 459. Aspar was an influential 5th century figure of Alan descent who served as magister militum and consul. By representing the power of the Germanic elements of the military, he dominated the Eastern court. Aspar helped secure the throne for Valentinian III and later did the same for Leo I. His influence was undercut by Leo’s alliance with Zeno, which eventually led to his execution in 471. While it is generally identified with the cistern that Aspar had built, it has also been  identified with the Cistern of Bonus.

The cistern is 152 meters on each side and is around 10-11 meters deep, while its brick and ashlar walls are around 5.2 meters thick. It had a capacity of as much as 250,000 cubic meters. It shared the same water supply line as the Aqueduct of Valens and the Cistern of Aetius. Brickstamps dating to the 5th century were found in the original masonry. At a later date, a water tower was added near its northwestern corner to help regulate water flow. By the 16th century it was used as a garden, which can be seen in its Turkish name Sultan Selim Çukurbostanı (“sunken garden” of Sultan Selim). Through most of the 20th century, there was a settlement in the cistern. In 2012, it was transformed into a public park.