 Between 1142 and 1170 the Knights Hospitaller undertook a building programme on the site . The castle was defended by a stone curtain wall studded with square towers which projected slightly . The main entrance was between two towers on the eastern side , and there was a <unk> gate in the northwest tower . At the center was a courtyard surrounded by vaulted chambers . The lay of the land dictated the castle 's irregular shape . A site with natural defences was a typical location for Crusader castles and steep slopes provided Krak des Chevaliers with defences on all sides bar one , where the castle 's defences were concentrated . This phase of building was incorporated into the later castle 's construction . 
