THE TANK-CATHEDRAL IN ISTANBUL: Built under the Roman Emperor Giustiniano’s will in 532 a.D.. Once used as a water tank for the Great Palace and the nearby buildings. It could contain until 80,000 ms cubic of water. When Costantinopolis was conquered by Ottomans, the water tank was closed. It remained forgotten until a researcher, whose curiosity was moved by the local old people stories describing how they provide themselves water lowering a bucket under their pavements, decided to investigate over this majestic water tank. The tank, sustained by decorated columns, is a very suggestive construction and due to water presence can create lots of reflections and light shades.