The cistern located in Gülhane Park dates from the 5th to 7th century. The cistern has a rectangular plan measuring around 17 x 12 meters with a depth of 7 meters. It has 12 columns (3 rows of 4 columns) with Corinthian capitals, which support a series of vaults. Its walls are lined with hydraulic mortar. Its function is uncertain, but it could have been connected to a monastery. Although it was once used as an aquarium (which partly accounts for its current configuration), it is now closed to the public.