The Cistern of Philoxenos, or Birbindirek Cistern, located between the Forum of Constantine and the Hippodrome of Constantinople in the Sultanahmet district. It has been restored and is now visited as a tourist attraction.
The cistern was constructed under a palace, often identified as the Palace of Lausos in the 4th century. The cistern is composed of a large hypostyle chamber supported by vaults. The 224 columns, each 14 to 15 meters tall, are made of marble from nearby Marmara Island. Each column is a superposition of two columns, joined by a marble ring. The floor of the cistern was later reinforced, so that only the upper column and a short sleeve of the lower column are thus visible. A part of the original exterior is is now preserved on display near the entrance. Most of the columns, and also the caps, are engraved with a Greek mason's mark.
The cistern was restored when the palace was completely destroyed in the 6th century. After the conquest of the city by the Ottomans in 1453, the cistern fell in to disuse, and was forgotten until rediscovered during the construction of Pasha Fazli's palace on the same site in the 17th century.