The Citadel of Carcassonne was at its zenith in the 12th century, and was the theatre
of the crusades against the Cathars (heretics) in the 13th century. It fell into decline
after the French-Spanish border was relocated in 1659. It was restored in the 19th century
by the architectural historian Viollet-le-Duc. It has 52 towers and two rings of town
walls making a total of 3km of battlements.