Basilica Cistern, Ancient Roman cistern in Fatih, Istanbul, Turkey
The Basilica Cistern is an underground Roman water reservoir beneath the Fatih district of Istanbul, extending roughly 138 by 65 meters. A total of 336 marble columns stand in regular rows and carry vaulted brick ceilings above shallow water.
Emperor Justinian I ordered the water reservoir built from 532 onward after the Nika uprising, to secure the water supply of Constantinople. Around 7,000 workers constructed the underground structure, which remained in use into the Middle Ages.
The two Medusa heads serve as column bases and were brought here from older temples. They lie sideways and upside down, showing how Byzantine builders reused Roman elements.
The entrance sits directly opposite Hagia Sophia and is easy to find. Raised wooden walkways lead through the interior, allowing you to walk among the columns without touching the water.
Small fish swim through the shallow water between the rows of columns and help maintain water quality. The basin originally held roughly 80,000 cubic meters (21 million gallons) of water and supplied the Great Palace.
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