Carcosa is a fictional city in Ambrose Bierce’s short story “An Inhabitant of Carcosa” (1886). The ancient and mysterious city is barely described and is viewed only in hindsight (after its destruction) by a character who once lived there. Its name may be derived from the medieval city of Carcassonne in southern France, whose Latin name was “Carcaso.”
American writer Robert W. Chambers borrowed the name “Carcosa” for his stories, inspiring generations of authors to similarly use Carcosa in their own works.
Source: Carcosa – Wikipedia