Located in the heart of France's Languedoc-Occitanie regions, 80 km (50 mi) southwest of Carcassonne, Montségur dominates a rock formation known as a pog — a term derived from the Languedocien dialect of Occitan — puòg or puèg, meaning "peak, hill, mountain."

[3] The murder of representatives of the inquisition by about fifty men from Montsegur and faidits at Avignonet, on 28 May 1242, was the trigger for the final military expedition to conquer the castle, the siege of Montségur.

In 1242 Hugues de Arcis led the military command of about 10,000 royal troops against the castle that was held by about 100 fighters and was home to 211 Perfects (who were pacifists and did not fight) and civilian refugees.

This idea was followed and expanded upon by various later writers, especially in France, and has inspired legends, conspiracy theories, and fictional works associating the Cathars and Montségur with the Holy Grail.

This often mentioned solar phenomenon, occurring in an alignment of two windows in the fortress wall, has been observed by hundreds of students, astronomers, spiritual pilgrims and locals alike who come to the chateau specifically to view it every year and has been recorded and included in the documentary "The Otherworld," (by Richard Stanley) in 2013.

The Groupe de Recherches Archéologiques de Montségur et Environs (GRAME) (Archeological Research Group of Montsegur and Vicinity), which conducted a 13-year archeological excavation of Montségur with minimal funds and the technology available at the time in 1964–76, concluded in its final report, which was not widely published, is not viewed as solid archeological research, and is hotly disputed by many, that: There remains no trace within the present-day ruins, neither of the first fortress which was abandoned before the 13th century (Montsegur I), nor of the one which was built by Raymond de Péreille around 1210 (Montsegur II)..." (Il ne reste aucune trace dans les ruines actuelles ni du premier château qui était à l'abandon au début du XIIIe siècle (Montségur I), ni de celui que construisit Raimon de Pereilles vers 1210 (Montségur II)...)[5]This small quote is all that can be found of this study, and no other study has been done.

[citation needed] The small ruins of the terraced dwellings, immediately outside the perimeter of the current fortress walls on the north-eastern flank are, however, confirmed to be traces of authentic former Cathar habitations.