The Basilica Cistern

  Located just south of the Hagia Sophia is the largest of several hundred cisterns beneath the city. Constructed in the sixth century during the reign of Justinian I (a Byzantine Emperor), the Basilica Cistern derived its name from the large public square on the first hill of Constantinople, the Stoa Basilica. Before there was a cistern on this spot, a Great Basilica was constructed here between the third and fourth centuries. Following several fires and civil unrests, the Basilica was removed and construction began on the cistern. Reportedly, 70,000 slaves were involved in the building of the cistern, which was to provide a water filtration system for the Great Palace of Constantinople and other buildings on the first hill. Surveys indicate that the cistern measures 453 feet by 212 feet (or 105,000 square feet) and can store upwards to 100,000 tons of water (although currently the capacity is kept at a much lower level).

There are 336 marble columns in the cistern. Each is 30 feet tall and they are arranged in 12 rows of 28 columns each, spaced 16 feet apart.

One column is engraved with pictures of a Hens eye, slanted branches, and tears. The tears are said to be a tribute to the hundreds of slaves that died during the construction process.

In the northwest corner of the cistern are two columns with block bases carved with the face of Medusa. The origins of these block bases are unknown.

Tradition holds that the blocks are oriented sideways and inverted in order to negate the power of the Gorgon's gaze.