The great Syrian fortress of Le Krak des Chevaliers, the best known, as it is on the whole the finest and best preserved, of the Crusader castles, has recently been made the subject of a brilliant and exhaustive study by M. Paul Deschamps; taken in conjunction with earlier notices by Rey, Van Berchem, T. E. Lawrence and others, this has left archaeologists in an exceptionally favourable position with regard to their knowledge of this castle. A few objections on points of detail might be raised to Deschamps' conclusions, but it appears to me that there is only one important question on which further clarification of our existing knowledge is needed : the reconstruction of the siege and capture of the Krak by the great Mamluk Sultan of Egypt, Bybars, in April 1271. The accounts given by the Arab historians of the period are not perfectly clear, and the explanations offered by Van Berchem and Deschamps do not appear to be the best possible, in view of the evidence of the fabric itself. In order to obtain a sounder idea of what occurred in the siege, it will first be necessary to consider the buildings and their history in brief.