The Basilica Cistern — the Yerebatan Sarnıcı, the "sunken palace" of Turkish report — is a drowned hall beneath the city the Turks call Istanbul, a warren of reservoirs and connecting tunnels whose oldest passages are older than the church that once stood above them. It was raised in the reign of Emperor Justinian to slake the thirst of the capital, and slakes it yet; one may still make out the hoist-holes cut in the floor and the iron rings set for rigging — mute witnesses to a long labour of water, and, one is left to suspect, to labours rather less innocent. The place is dry now, and wonderfully preserved, its roof upheld by a whole forest of columns.
Those of the company who ventured into it found the water-court less peaceful than its stillness promised. A Janissaries soldier lay freshly slain amidst the marks of a struggle, and a jammed door gave way only to magic; beyond it stood an old store-room crowded with wooden chests, where a giant spider fell upon one of their number. A steep stair let down to a corridor in which a human skull was seen to move of its own accord — and thereupon came the walking dead, animate skeletons and a desiccated horror, to be put down by main force. Here too they met a living Janissary, one Alexander, who bade them quit the place; and, prudent in the matter of the unquiet dead, they gave the remaining bodies to the fire lest more should rise.
It has since come to light that the cistern keeps a far older prisoner. The Shahmeran has lain bound here by potent workings since the days of Justinian and his empress Theodora, and it was in that same reign that she and her spellcasters were last met in battle and thrown down.