The castles built by the crusaders are the most imposing military works of the Middle Ages and the Krak des Chevaliers is the most imposing of the castles.
The Krak, which held out for over 150 years, stuck—in the words of a contemporary chronicler—like a bone in the throats of the Muslims, who surveyed with dismay the monstrous 80-foot-thick wall on its south side, and christened it "the Mountain." On at least 12 occasions the Saracens beseiged the castle without success and when, with a depleted garrison, it fell in 1271 to the Sultan Beibars, it fell not by assault but by cunning. A forged letter was conveyed into the castle, purporting to come from the Grand Commander at Tripoli, instructing the knights to surrender. They did so, and on April 8th the garrison marched out under safe-conduct to the coast.
Krak is a measure of the defensive skill of the Franks. It embodies in supreme fashion every protective device then known, and it epitomizes the rapid development of military architecture in the Holy Land. One of the first medieval castles with fully concentric fortification. Krak was immensely strong. Substantial towers provided complete flanking fire along the outer curtain. The wall top, moreover, was furnished with the earliest known example of continuous machicolation. The walls of the inner ward were strengthened by a massive talus, and at the point of greatest danger was set a formidable keep-fortress composed of three linked towers. All the masonry was the finest ashlar, and the stone blocks of the inner ward are often a yard long and average 1 feet in height. Reference has already been made to the cunningly defended entrance. The vaulted passage, which was the only means of access to the inner ward, contained three "elbows" and was defended by machicoulis, by four gates, and at least one portcullis. Yet the Krak was as elegant as it was strong. Its Romanesque chapel, its traceried Gothic arcading, and the vaulted and pilastered chamber of the Grand Master embodied the genius of the medieval masons who built the cathedrals of France. No wonder that Lawrence of Arabia pronounced Krak to be "the most wholly admirable castle in the world."