Walls would generally have been made of compacted earth faced with stone to prevent mining by the enemy sappers. In the Crac however, the inner wall rising from the moat is built of stone right down to the bed-rock. Moreover, the stone slabs are remarkably smooth and fit together perfectly to give an unclimbable surface. T.E. Lawrence, while visiting the Crac as an undergraduate tried several times to scale the slope but never got more than a third of the way up before sliding back down again. Of course the presence of defenders above dropping rocks and molten lead would not have made the task any easier. This slope is one of the Crac's most formidable defensive features and was in part responsible for its reputation as the best defended castle in Christendom.