This research aims at sheding light on the fortress of petra Deserti castle during the occupation of crusades form its establishment in 537A.H./ 1142A.D. in the reign of the crusade King Fulk Anjou (526- 538 A.H / 1131- 1143A.D.)
The research also deals with the reasons that have been behind its building and the results caused from that. In addition to following the crasade rulers who succeed to its reign and the out standing of them Renaud Chatillon, whose reign forms an important turning point on the political, military and economic fields.