The origins of the Knights Hospitaller are unclear , but the order probably emerged around the 1070s in Jerusalem . It started as a religious order which cared for the sick , and later looked after pilgrims to the Holy Land . After the success of the First Crusade in capturing Jerusalem in 1099 , many crusaders donated their new property in the Levant to the Hospital of St John . Early donations was in the newly formed Kingdom of Jerusalem , but over time the order extended its holdings to the Crusader states of the County of Tripoli and the Principality of Antioch . Evidence suggest that in the 1130s the order became militarized when Fulk , King of Jerusalem , granted the newly built castle at Bethgibelin to the order in 1136 . A papal bull from between 1139 and 1143 may indicate the order hiring people to defend pilgrims . There was also other military orders , such as the Knights Templar , which offered protection to pilgrims .