The Knights of St. John evolved during the Crusades from a monastic order that provided hostels for Christian pilgrims visiting Jerusalem. The need to provide armed escorts to the pilgrims began their transformation into a Military Order. Their fervor and discipline defined them as an elite component of most Crusader forces, and the Knights Hospitaller (as they were known) participated in nearly all major conflicts, including Hattin, Acre, and Arsuf. After the recapture of the Crusader Kingdoms by the Muslims, the Order continued to fight from a new base, initially in Rhodes and then in Malta. Moving to the sea, the Knights became one of the great naval powers in the Mediterranean, defending Christian merchant shipping from Barbary pirates (and increasingly turning to piracy as funding from their estates in Europe dwindled). They provided a critical defense against Islamic expansion in the Mediterranean, decisively resisting a massive siege of Malta by the Ottoman Turks in 1565. The Order remained an important power in the Mediterranean until its defeat by Napoleon in 1798.