Upon the fall of Acre in 1291 they retired to Venice where Emperor Frederick II commissioned them to convert the heathens in Prussia, Lithuania, and Estonia, becoming a very successful order headquartered in Marienburg from 1309-1509.
The Oath of the Medieval Teutonic Knights
The oath of the Medieval Teutonic Knights was as follows:
"I... do profess and promise chastity, giving up all property, and obedience to God and the Blessed Virgin Mary and to you, Brother ... Master of the Teutonic Order, and to your successors, according to the Rules and Regulations of the Order. And I will be obedient to you, and to your successors, even unto death."
Teutonic Knights History
Teutonic Knights side with Hospitallers and barons in Acre against the Templars in 1209 which becomes the origin of long-standing opposition between the Templars and Teutonic Knights. In 1217 Frederick II granted the Teutonic Knights the same status as the Templars and Hospitallers in the Kingdom of Sicily. In 1220 Pope Honorius III gave privileges to the Teutonic Knights; as an order, they now were on the same level as the Templars and the Hospitallers. In 1226 the "Golden Bull of Rimini" from Frederick II for the Teutonic Knights giving them wide-ranging authority in the name of the empire in Prussia. In 1319 the Teutonic Knights' headquarters moved from Venice to Prussia. In 1410 Lithuanian-Polish forces defeated the Teutonic Knights at the Battle of Tannenberg, Prussia, halting the Teutonic Knights’ eastward expansion along the Baltic and hastening their decline.