The fort is perched at 1207m (3000 feet) above sea level and sits on a rock formation known as a "pog" which is derived from the Occitan words "pueg" or "puog" meaning peak, hill or mountain.

It is believed that there was human settlement in the area in the Stone Age period, 80,000 years. There is also evidence of Roman occupation; Roman currency and tools have been found around the site. In the Middle Ages Montsegur was ruled by the Counts of Toulouse, the Viscounts of Carcassonne and then the Counts of Foix. In 1243/44 the Cathars were besieged at Montsegur at the end of the Albigensian Crusade by 10,000 French troops. The Cathars finally surrended in March 1244 and about 220 were burned in a large bonfire at the foot of the hill when they refused to renounce their faith.

A short time before the fall of Montsegur it is believed that the some of the Cathars apparently slipped through French lines and carried away a mysterious "treasure." It has never been discovered what it was or what became of it, but there is much speculation that it might have actually been the Holy Grail. Montsegur is often named the Holy Grail castle because a book named Parzival written by Wolfram von Eschenbach talks about a castle Monsalvat, similar to Montsegur with the same meaning "safe mountain, secure mountain."  More can be read about Montsegur and the Holy Grail in the book written by Dan Brown, "The Da Vinci Code."

There is also belief that Montsegur has solar alignment characteristics which is said to be visible on the morning of the summer solstice. Allegedly this solar phenomenon occurs in an alignment of two windows in the fortress wall. This has not be scientifically surveyed, measured, recorded or confirmed. There was also a 13 year archeological excavation at Montségur between 1964 and 1976 and there was no trace within the current ruin of the first fortress which was abandoned before the 13^th century, nor of the one built by Raymond de Péreille around 1210. However, small ruins of the terraced dwellings immediately outside the current fortress walls on the northeasten flank showed up traces of authentic former Cathar habitations.

Montaillou or Montalhon in Occitan is a small village in Sabarthès area of the Ariege. Montaillou was one of the last bastions of the Albigensian heresy and the Bishop of Pamiers, Jacques Fournier launched an extensive inquisition to search out Cathars over a 30 year period from 1294 until 1324. . In 1318 the whole village was arrested on the orders of the bishop. Fournier retained the records of the inquisition and when he became Pope he took them to the Vatican in Rome which is where they remain today.

The Château de Montaillou stands as a ruin in the village standing on the slope of Mount Allion – it has been made famous in Emmanuel Le Roy Ladurie’s book, "Montaillou, village Occitan." The chateau was built by the lords of Alion at the end of the 12^th century. There is not much left of the ruin to be seen is a ruined tower, evidence of walls of the keep and a part of a curtain wall which surrounded the courtyard. Dry moats to the north and east provided defence and the very steep southern slope was sufficient.

Bernard d’Alion, one of the lords of Alion, paid hommage to the King of France in 1226 but his sympathies still remained with the Cathars. He married Esclarmonde who was the daughter of Roger IV, Count of Foix in 1236. In 1258, Bernard was condemned by the Inquisition as a Cathar and burned alive in Perpignan. The castle was then take by of Roger IV, Count of Foix and became a frontier fortress between the County of Foix and the French King’s land and Aragon. At the end of the 13^th century, the Count increased the thickness of the walls of the castle, it survived the Albigensian Crusade but fell into disrepair later. The Château de Montaillou became listed as a "monument historique" in 1984.

Foix (see "Nearby Towns & Villages")