The leaden sky pressed in on the mosque's tall, vigilant minarets, and on its multiple helmet-like grayish blue domes, on whose top black birds alighted. From a vantage point on the mosque's outer wall, one can look down to tiers of the same grayish blue domes, forming a terrace that seems to have extended all the way to the Aegean Sea and is punctuated by nothing but more white, slender minarets.

The mood is solitary, brooding, even apocalyptical.

But to feel dark power one has to burrow further into history, literally. The vast, barelylit chamber of the Basilica Cistern just southwest of Hagia Sophia is where people marvel at what the ancestors were capable of building, with the same amazement and disbelief they might have shown toward the Great Wall of China or the pyramids of Egypt.

Covering 9,800 square meters and with a water storage capacity of up to 100,000 tons, the rectangular-shaped cistern was built in the sixth century to supply water to the capital of the Byzantine Empire. In an engineering feat, the ceiling weight is distributed through arches to 336 giant columns, each 9 meters high and lined in 12 rows.

The locals call it "the sunken palace". Anyone who has descended the 55 steps of staircase to stand at the doorstep of this palace must feel that this is one presided over by Hades, the Grecian god of the dead and king of the underworld. If you want proof look for the two Medusa heads used as plinths in the southwestern part of the cistern.