The Teutonic Order was a crusading order of knights under religious vows who were formed at the end of the 12th century in Palestine to give medical aid to pilgrims to the holy places. They received papal orders for crusades to take and hold Jerusalem for Christianity. They were based at Acre. They later transferred their area of interests to the Baltic Sea and Prussia. The Order had many wars against Poland and Lithuania and Tatars. The biggest battle of the Teutonic Knights was the Battle of Tannenberg (in Polish Battle of Grunwald), which they lost . The burgers of Prussia rose up against the Catholic Teutonic order and their power waned .The emperor Maximilian I Habsburg had made an agreement with the Polish king and in 1525, the grand master of the order, Albrecht Hohenzollern of Brandenburg converted to Lutheranism and swore allegiance to the Polish king, who made him the Duke of Prussia. This "Polish king" was the grand duke of Lithuania Sigismund I Jagiello and was the brother of Albrecht of Brandenburg-Prussia's mothers.