As soon as the Knights Hospitaller purchased the land they began construction of Belvoir Castle. While Gilbert of Assailly was Grand Master of the Knights Hospitaller the order gained around thirteen new castles, among which Belvoir was the most important. The fortress of Belvoir served as a major obstacle to the Muslim goal of invading the Crusader Kingdom of Jerusalem from the east. It withstood an attack by Muslim forces in 1180. During the campaign of 1182, the Battle of Belvoir Castle was fought nearby between King Baldwin IV of Jerusalem and Saladin.