La Cite is the largest compelete fortification in Europe. First signs of settlement in the region date to about 3500 BC, but the hill site of Carsac became an important trading place in the 6th century BC.
Cathars being expelled from Carcassonne in 1209
Carcassonne was strategically identified and Romans fortified the hilltop around 100 BC and eventually made it the colonia of Julia Carsaco, later Carcasum. The main part of the lower courses of the northern ramparts dates from Gallo-Roman times.
In 462 the Romans officially ceded Septimania to the Visigothic king Theodoric II who had held Carcassonne since 453. He built more fortifications at Carcassonne, which was a frontier post on the northern marches; traces of them still stand. Theodoric is thought to have begun the predecessor of the basilica that is now dedicated to Saint Nazaire.
In the 11th century the Trencavel family allied in succession either with the counts of Barcelona or of Toulouse. They built the Château Comtal and the Basilica of Saint-Nazaire. In 1096 Pope Urban II blessed the foundation stones of the new cathedral, a Catholic bastion against the Cathar heretics.
He added to the fortifications and Carcassonne became a border citadel between France and Aragon. In 1240 Trencavel's son tried to reconquer his old domain but in vain. The city submitted to the rule of kingdom of France in 1247, and King Louis IX founded the new part of the town across the river.
The antiquary and mayor of Carcassonne, Jean-Pierre Cros-Mayrevieille, and the writer Prosper Mérimée, the first inspector of ancient monuments, led a campaign to preserve the fortress as a historical monument. Later in the year the architect Eugène Viollet-le-Duc, already at work restoring the Basilica of Saint-Nazaire, was commissioned to renovate the place.
In 1853, works began with the west and southwest walling, followed by the towers of the porte Narbonnaise and the principal entrance to the cité. The fortifications were consolidated here and there but the chief attention was paid to restoring the roofing of the towers and the ramparts, where Viollet-le-Duc ordered the destruction of structures that had encroached against the walls, some of them of considerable age. Viollet-le-Duc left copious notes and drawings at his death in 1879, when his pupil Paul Boeswillwald, and later the architect Nodet continued the rehabilitation of Carcassonne.
The restoration was strongly criticized during Viollet-le-Duc's lifetime. Fresh from work in the north of France, he made the error of using slates and restoring the roofs as pointed cones, where local practice was traditionally of tile roofing and low slopes, in a snow-free environment. Yet, overall, Viollet-le-Duc's achievement at Carcassonne is agreed to be a work of genius, though not of strictest authenticity. Fortifications consists of a double ring of ramparts and 53 towers.