Soon after the Erkelenz was elevated to a town status in the 12th century, work began on the brick fortifications of the place. These probably consisted of basic ramparts as had been common since time immemorial for the defence of settlements. Although the castle was not documented until 1349, the town appeared to have developed under the protection of the castle.
The castle has 23 high keep, curtain walls and corner towers. It was part of larger city walls. It was badly damaged by French army in 1674.
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.