The Augustinian priory here was founded in 1080, on land donated by the Alquier noble family of Béziers. A new church was consecrated in 1115. Numerous relics were collected by the abbey and it served as cemetery to the nobility of the region. The lands owned by the priory extended to 75 villages. Pope Innocent III in the context of the crusade against the Cathars exempted the priory from control by the bishops of Béziers, making it subject only to the Holy See in spiritual matters. In secular terms, the abbey pledged allegiance to Louis IX of France in 1268.
In the 14th century the priory began to decline, as a result of the Black Plague and the turmoils of the Hundred Year's War, and the number of monks halved, from 80 in the 13th century to 40 by 1384. The monastery was pillaged during the wars of religion, in 1539, and again in 1563. By 1605, the monastic community was moribund, reduced to seven or eight monks. In 1671, it was attached to Sainte-Geneviève abbey in Paris.
The medieval buildings were torn down and the estate was rebuilt from ground in the mid-18th century under prior Pas de Beaulieu, except for the church building, which was modified but retains its 12th century romanesque core structure. After the French revolution, the monastery was dissolved and the property nationalised, in 1791 sold to an advocate, Marc Antoine Thomas Mérigeaux, who bought it on behalf of a Prince de Conti who offered it to his mistress, Madame de Brimont.
From this point, the former monastery became known as Château de Cassan or Cassan castle. It changed hands several times during the 19th and 20th centuries, eventually passing to the French state, housing administrative offices, but in 1995 sold again to a private party, and in 2002 to a real estate holding.
References:The Château de Foix dominates the town of Foix. An important tourist site, it is known as a centre of the Cathars. Built on an older 7th-century fortification, the castle is known from 987. In 1002, it was mentioned in the will of Roger I, Count of Carcassonne, who bequeathed the fortress to his youngest child, Bernard. In effect, the family ruling over the region were installed here which allowed them to control access to the upper Ariège valley and to keep surveillance from this strategic point over the lower land, protected behind impregnable walls.
In 1034, the castle became capital of the County of Foix and played a decisive role in medieval military history. During the two following centuries, the castle was home to Counts with shining personalities who became the soul of the Occitan resistance during the crusade against the Albigensians.