 The Hospitallers began rebuilding the castle in the <unk> and were finished by 1170 when an earthquake damaged the castle . The order controlled a number of castles along the border of the County of Tripoli , a state founded after the First Crusade . Krak des Chevaliers was among the most important , and acted as a center of administration as well as a military base . After a second phase of building was undertaken in the 13th century , Krak des Chevaliers became a concentric castle . This phase created the outer wall and gave the castle its current appearance . The first half of the century has been described as Krak des Chevaliers ' " golden age " . At its peak , Krak des Chevaliers housed a garrison of around 2 @,@ 000 . Such a large garrison allowed the Hospitallers to extract tribute from a wide area . From the 1250s the fortunes of the Knights Hospitaller took a turn for the worse and in 1271 Mamluk Sultan Baibars captured Krak des Chevaliers after a siege lasting 36 days , supposedly by way of a forged letter purportedly from the Hospitallers ' Grand Master that caused the Knights to surrender . 
