There are several hundred ancient underground cisterns in Istanbul that were used to provide a stable water supply. The Basilica Cistern is the largest.
One of the other cisterns, "discovered" recently - in the 1600s - was well known by some local residents. Some people in a certain part of town were known to go fishing through a hole in their basement floor. A researcher who was looking for evidence of a rumored cistern stumbled upon a local who said something like "Oh yeah, that's under my house." Then the local guy took him down to his basement, got in a boat and toured the huge cistern and its columns as the local guy fished from the boat.
The Basilica Cistern was built in the 6th century under the Byzantium reign of Emperor Justinian. The cistern was originally a Basilica, a Roman public building, built between the 3rd and 4th centuries. It was used as a commercial, legal, and artistic center. There are 336 columns supporting the ceiling, each column is 30 feet tall. The cistern was capable of storing 2,800,000 cubic feet of water.
One of the columns is engraved with tears. Ancient texts suggest the tears pay tribute to the hundreds of slaves who died building the cistern. Also according to ancient texts, 7000 slaves were used for this project which supplied water to the palace and other buildings in this part of town. The cistern continued to supply water for many centuries, into modern times.
Walkways for visitors weave through the columns.
Moist stone floors.
Amazing what can be done when you have 7000 slaves working for you.
In the far back corner of the cistern, two columns have a base made of Medussa's head. The head is turned upside down on one column (above) and sideways on the other. No one knows for sure why. The sideways head might have been placed that way to adjust the height of the column. The upside-down head might have been a superstitious decision. According to one popular theory, it was to negate the power of the Gorgon's gaze, which can turn you into stone. Medussa is one of three Gorgon sisters.