Istanbul: Sultanahmet - Yerebatan Saray (Sunken Palace), Cistern Basilica

Cities in ancient and medieval times were always in danger of siege. In a siege, the main problem was inadequate supply of food and water.
The Roman and Byzantine emperors built huge cisterns to solve this problem. The cistern well known under the designation ' into the earth sunk palace ' is with lateral dimensions of 138 x 85 m and a capacity of 80.000 m³ and its 336 marble columns is the largest under numerous underground Istanbul’s water reservoirs.
Under Justinian at the same time with the neighbouring Hagia Sophia established cistern had been rediscovered after intermediate burying 1545