 When the outer walls were built in the 13th century the main entrance was enhanced . A vaulted corridor led uphill from the outer gate in the northeast . The corridor made a hairpin turn halfway along its length , making it an example of a bent entrance . Bent entrances were a Byzantine innovation , but that at Krak des Chevaliers was a particularly complex example . It extended for 137 metres ( 450 ft ) , and along its length were murder @-@ holes which allowed defenders to shower attackers with missiles . Anyone going straight ahead rather than following the hairpin turn would emerge in the area between the castle 's two circuits of walls . To access the inner ward , the passage had to be followed round . 
