The Château de Montségur is a former fortress near Montségur, a commune in the Ariège department in southern France. Its ruins are the site of a razed stronghold of the Cathars. The present fortress on the site, though described as one of the "Cathar castles," is actually of a later period. It has been listed as a monument historique by the French Ministry of Culture since 1862.

Ariège is a department in southwestern France, located in the region of Occitanie. It is named after the river Ariège and its capital is Foix. Ariège is known for its rural landscape, with a population of 153,287 as of 2019. Its INSEE and postal code is 09, hence the department's informal name of le zéro neuf. The inhabitants of the department are known as Ariègeois or Ariègeoises.