Qalaat Marqab. Syria. View of archaeologists excavating and restoring and a section of the crusader castle. Qalaat Marqab or Marqab citadel is a formidable black basalt Crusader castle that is sits upon an extinct volcano peak with commanding views over the Syrian coastal plain and the Mediterranean. The site was originally built upon by the Muslims in 1062 and eventually fell into the hands of the Crusaders and then the Knights Hospitaller around the twelfth century. The Hospitaller knights converted the fortress in to one of the Crusader strongpoints using fortification concepts that were unique for their time. The impregnable castle only fell into the enemy hands due to the Crusaders dwindling manpower resources in the thirteenth century.