From Wikipedia...

The Châteaux de Lastours (in Occitan Lastors) are four so-called Cathar castles in the French commune of Lastours in the département of l'Aude. The four castles are on a rocky spur above the village of Lastours, isolated by the deep valleys of the Orbeil and Grésilhou rivers.

They were built at an altitude of 300 m along a rock wall just 1300 feet (~400 m) long by 165 feet (~50 m) wide. Cabaret, Surdespine and la Tour Régine stand in line, while Quertinheux is built on a separate pinnacle close by. The site has been classified monument historique (historic monument) by the French Ministry of Culture since 1905 and archaeological digs are still in progress.

These four castles constitute a single entity, even though they are not a single structure. The natural layout of the site permitted the economy of a fortress of great height. Plans were adapted to the rocks on which they were built. The construction of each is different reflecting the range of alterations made to the castles.