The Order of the Knights of Saint John of Jerusalem , also known as Order of Saint John, Order of Hospitallers, Knights Hospitaller, and the Hospitallers, was the name of the precedent medieval military organisation of the contemporary Sovereign Military Order of Malta, one of the most prominent of the Roman Catholic military orders and still today a sovereign subject of international law. It was headquartered in the Kingdom of Jerusalem, Rhodes and Malta, until it became known by its current name.