No traveler to the Fade can fail to spot the Black City. It is one of the few constants of that ever-changing place. No matter where one might be, the city is visible. (Always far off, for it seems that the only rule of geopgraphy in the Fade is that all points are equidistant from the Black City.)
The Chant teaches that the Black City was once the seat of the Maker, from whence He ruled the Fade, left empty when men turned away from Him. Dreamers do not go there, nor do spirits. Even the most powerful demons seem to avoid the place.
It was golden and beautiful once, so the story goes, until a group of powerful magister-lords from the Tevinter Imperium devised a means of breaking in. When they did so, their presence defiled the city, turning it black. (Which was, perhaps, the least of their worries.)
--From Beyond the Veil: Spirits and Demons, by Enchanter Mirdromel.