 Krak des Chevaliers can be classified both as a spur castle , due to its site , and after the 13th @-@ century expansion a fully developed concentric castle . It was similar in size and layout to <unk> Jacob , a Crusader castle built in the late <unk> . Margat has also been cited as Krak des Chevaliers ' sister castle . The main building material at Krak des Chevaliers was limestone ; the ashlar facing is so fine that the mortar is barely noticeable . Outside the castle 's entrance was a " walled suburb " known as a <unk> , no trace of which remains . To the south of the outer ward was a triangular <unk> and the Crusaders may have intended to build stone walls and towers around it . It is unknown how it was defended at the time of the 1271 siege , though it has been suggested it was surrounded by a timber palisade . South of the castle the spur on which it stands is connected to the next hill , so that siege engines can approach on level ground . The inner defences are strongest at this point , with a cluster of towers connected by a thick wall . 
