The Order of Knights of the Hospital of Saint John of Jerusalem, commonly known as the Knights Hospitaller, is a Catholic military order. It was founded in the crusader Kingdom of Jerusalem in the 12th century and had its headquarters there, in Jerusalem and Acre, 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).