Throughout the centuries the historic site of Carcassonne has played a decisive role in the history of Languedoc. An Iron Age Oppidum transformed into a Roman town in the Ist Century BC, the city-state became the possession of the powerful Viscount Trencavel who ruled over Bas-Languedoc. At the end of the crusade against the Albigensians the city, with its improved fortifications, became one of the strongholds symbolising royal power on the frontier between France and Aragon. However, after the Treaty of the Pyrenees made the Roussillon a French possession, the city lost its strategic role and its defence works were neglected. In the XIXth Century, the residents of Carcassonne and the Historic Monuments Department (Service des Monuments historiques), commissioned Eugène Viollet-le-Duc to restore the ancient fortress to its original appearance.