A medieval Teutonic Knight was a member of the Catholic military Deutscher Orden or Teutonic Order, officially founded in March 1198 CE. The first mission of the Teutonic knights was to help retake Jerusalem from the Arabs in the Third Crusade (1187-1192 CE), and during this failed attempt they set up a hospital outside Acre during the siege of that city. The hospital was granted the status of an independent military order by the Pope, and the knights never looked back. The Middle East proved to be too difficult to hold onto, but the ambitious order merely switched their focus to converting Christians and grabbing land in central and eastern Europe instead. With their famous black cross on a white tunic, the austere Teutonic knights became master traders and diplomats, carving out vast swathes of territory from their base in Prussia and building castles across Europe from Sicily to Lithuania.
Foundation: The Third Crusade
The Third Crusade was called by Pope Gregory VIII following the capture of Jerusalem in 1187 CE by Saladin, the Sultan of Egypt and Syria (r. 1174-1193 CE). Although led by the cream of Europe's nobility, the project was beset with problems, none bigger than the accidental death en route of Frederick I Barbarossa (King of Germany and Holy Roman Emperor, r. 1152-1190 CE). Barbarossa's untimely drowning resulted in most of his army trudging back home in grief, but some German knights pressed on and assisted in the siege of Acre which terminated in July 1191 CE. Despite other successes, the Crusaders only managed to get within sight of Jerusalem and no attempt was made to attack the holy city. Instead, control of a small strip of land around Acre was negotiated and the future safe treatment of Christian pilgrims to the Holy Land.
