The Basilica Cistern is a covered water store under the old city of İstanbul, which dates from 526–27 under Justinian. It lies on Soğukçeşme Sokağı, south-west of Hagia Sophia and beside the Milion, the stone the Byzantine empire treated as the zero point of the world. Rows of marble columns stand in its water, and among them are carved Medusa heads set upside down. Turkish has given the place two names, and each one explains part of what you are looking at.
Two names, one building
Yerebatan Sarayı means the sunken palace, a name that comes from the marble columns rising out of the water like the hall of a palace. Basilica Cistern, the other name, comes from what stood overhead. A monumental building called the Basilica Stoa is believed to have occupied the ground above, and the cistern is thought to have been made to serve it as well as the district around it.
How it was built
The builders excavated the courtyard of the imperial stoa down to bedrock to make the storage space. Rows of columns went in, arches joined them, and vaults closed the roof. The whole is a rectangular brick structure sitting on rock, and it holds about 100,000 tons of water.
The figures are simple to remember. There are three hundred and thirty-six columns, set in twenty-eight rows from east to west and twelve from north to south, and they hold up the brick vaults. Forty-one of them can no longer be seen, because they stand in the north-western part that was walled off under Abdülhamid II. The German archaeologist Eckhard Unger was first to measure it, during the First World War, and his figures were 138 by 64.6 metres.
Medusa and the decorated columns
Not all the columns are plain. The cistern contains decorated shafts and Corinthian capitals as well as the inverted Medusa heads.
A working part of the city's water
The cistern was not a monument when it was made. It was linked to the Hadrianic water lines that supplied the ground between the city's first two hills. Once the Ottomans took the city it became a distribution point serving Sarayburnu and Bahçe Kapısı, a role that changed in part once the Ottomans had built their own water works and repaired the old Byzantine conduits.
Its name stayed in the neighbourhood after that. The quarter that grew over it kept the word, and so does Yerebatan Caddesi, the street that links Cağaloğlu with Divanyolu and Hagia Sophia's square. Close neighbours in the same district include two other cisterns, Binbirdirek and Şerefiye, and the Achilles and Zeuxippus baths, so it belongs to a much wider underground and imperial landscape. Hagia Sophia is the obvious visit to pair with it, a short way to the north-east.
