The Basilica Cistern is the largest of hundreds of underground cisterns in Turkey and the last surviving structure of its kind in Istanbul. The impressive space is capable of holding 80,000 cubic metres of water. It is located in the Sultanahmet district in the centre of Istanbul next to the famous converted cathedral and museum, Hagia Sophia. The Basilica Cistern has a grand total of 336 marble columns in a linear arrangement; 12 rows, each with 28 columns, many of these columns were taken from various Ruined Temples in Turkey, primarily from ancient sites located in the Izmir province on Turkey's Aegean coast; for this reason, you can see mismatched decorative cornices at the tops of many of the columns. Waterproofing and other repairs are constantly being made to these columns and to the walls of the cistern.
The underground cistern was built during the Byzantine Empire, by the Emperor Justinian in the 6th century. The Basilica Cistern provided water for the Great Palace of Constantinople and other buildings on the hill and continued to provide water long after the Ottoman conquest in 1453.
Inside there are two Medusa heads of unknown origin carved into stone blocks. One of the heads is tilted on its side, whilst the other is upside down the heads can be seen in the deepest part of the cistern, both grotesque faces stare eerily outwards in the dim light. A visit to the Basilica Cistern will be quite a contrast, you will leave behind the blue sky and the pretty fountains of the central square as well as the pointed minarets of the Blue Mosque and descend into the gloomy light of the cistern. A metal boardwalk has been installed a foot or two above the ground so you can walk through the same sombre space where the James Bond movie, From Russia With Love, was filmed. Venture to the darkest corner and find large fish swimming in the black waters.