The organization became a military religious order under its own papal charter, charged with the care and defence of the Holy Land. Some scholars consider the Amalfitan order and hospital to have been distinct from Gerard's order and its hospital. After the conquest of Jerusalem in 1099 during the First Crusade, a group of crusaders formed a religious order to support the hospital.

Blessed Gerard, a lay brother of the Benedictine order, became its head in 1080. Earlier in the 11th century, merchants from Amalfi founded a hospital in Jerusalem dedicated to John the Baptist to care for sick, poor, or injured pilgrims to the Holy Land. The Hospitallers arose in the early 12th century during the height of the Cluniac movement, a reformist movement within the Benedictine monastic order that sought to strengthen religious devotion and charity for the poor. It was founded in the Kingdom of Jerusalem in the 12th century and had headquarters there until 1291, thereafter being based in Kolossi Castle in Cyprus (1302–1310), the island of Rhodes (1310–1522), Malta (1530–1798), and Saint Petersburg (1799–1801).

The Order of Knights of the Hospital of Saint John of Jerusalem ( Latin: Ordo Fratrum Hospitalis Sancti Ioannis Hierosolymitani), commonly known as the Knights Hospitaller ( / ˈ h ɒ s p ɪ t əl ər/), was a medieval and early modern Catholic military order. Jean Parisot de Valette, Philippe Villiers de L'Isle-Adam, Garnier de Nablus

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