Istanbul’s Ancient Basilica Cistern

This isn’t just any old water tank. Buried under the streets next to Hagia Sophia might well be the most impressive water tank you’ll ever see. Its purpose was entirely functional. Built during the reign of Byzantine Emperor Justinian (527-565), it provided water to the imperial palace and local residents of Constantinople.

It is 140 meters long and 70 meters wide, with brick walls nearly 5 meters thick and the brick floor covered in Khorasan mortar to make it waterproof. It has the capacity to hold 100,000 tons of water. Above it once stood a basilica, now long gone.

The cistern’s builders could have been content at the engineering feat of building such an impressive underground tank in the middle of a city, let alone transporting the water from the Belgrade Forest 19 kilometers away over a series of aqueducts.

But they decided to also show off their ornamental skills by recycling marble columns from other structures, creating what became popularly known as the Sunken Palace. There are 336 marble columns, each 9 meters high, arranged in 12 rows of 28 columns. Brick arches distribute the ceiling’s considerable weight evenly over the columns. And to top it off, they added two Medusa’s heads, themselves fine examples of Roman Period art. It’s not known where they came from or why they were installed, although over the centuries a number of legends have been used to explain them.

After the Ottomans took over Istanbul in 1453, the water was used in the gardens of Topkapi Palace–the Ottoman’s preferred running water over stagnant water and installed their own water supply system for drinking and cooking water. The cistern became largely forgotten until a Dutch traveler, P. Gyllius, rediscovered them in the mid-16th century.

These days the Basilica Cistern is preserved only as an historic landmark. Wooden walkways have been installed, with a few lights to illuminate the gloom. Large fish still cruise the shallow waters, darting in and out of the light.

Photos of the Basilica Cistern

What to Know Before You Go

• It’s damp down here. It’s also slippery. The Turks have mastered many things over the millennia, but the non-skid surface isn’t one of them. So watch your step not only the stairs but also on the walkways.
• The Basilica Cistern is relatively compact and can be comfortably visited in a half hour or less.
• It’s very close to both Hagia Sophia and the Blue Mosque.