The Yerebatan Cistern was built by Byzantine Emperor Justinianus in the 6th century. The cistern measures 140x70 meters, and is one of the most important Byzantine works that have survived the years.
It was also used by Ottomans, since the collection and storage of water has always been one of the major challenges of Istanbul. Today Yerebatan cistern has been emptied down to a meter deep, and a walkway has been built inside turning the cistern into a very interesting touristic attraction. One of the most interesting things about this cistern is the fact that many stones used in its construction were taken from other historical structures.