There are many cisterns in Istanbul but this is the biggest ever found. Yerebatan Sarayi, or Sunken Palace, the cathedral-sized Cistern runs beneath the entire street and some buildings. This is an underground chamber of 138 x 64.6 metres. The large space is formed by supporting a ceiling vault and arch system by a forest of 336 marble columns. The ceiling vaults, known as Manastır Tonozu (cloister vault), are built without using a mould. From whatever angle you view, the perspective view of the columns and ceiling arches give you a very strong geometrical feel . . . . . . . . . . . . .. . . . .