On the track of historyAround 780, Charlemagne, king of the Franks, erected a stone church on the banks of the river Hase (the nucleus of today's Osnabrück). The city's name is presumably a combination of the Low German words "Ossen" (ox) and "Brügge" (bridge).
Some time before 803, the city became seat of the Prince-Bishopric of Osnabrück, which likely makes the city the oldest bishopric in Saxony. It is thought that, in 804, Charlemagne possibly founded the Gymnasium Carolinum (a secondary school) which would make it Germany's oldest "Gymnasium". But the charter with the date is disputed and could be a forgery. As a hub of old trading routes and as the seat of a bishop, Osnabrück developed into a thriving center for commerce in the Middle Ages. Shortly afterwards, in 1157, Emperor Frederick Barbarossa granted the city its "Befestigungsrecht" (fortification privileges). Most of the towers that were part of the medieval fortification are still visible in the city.
From 1412-1669, Osnabrück was a member of the Hanse (Hanseatic League), the most important trading trust of its time, as well as a member of the Westphalian Federation of Cities.
From1633 -1643 the city was under Swedish occupation, and from 1643-1648 negotiations in Münster and Osnabrück led to the Peace of Westphalia. The two cities are about 35 miles apart in the present-day German states of North Rhine-Westphalia and Lower Saxony. Sweden had favored Osnabrück due to its Protestant background, while France chose Münster due to its Catholic background.
The two locations were required because Protestant and Catholic leaders refused to meet each other. The Catholics used Münster, while the Protestants used Osnabrück. The Peace of Westphalia was proclaimed on October 25, 1648, and until 1803 Catholic and Protestant bishops alternated in ruling the bishopric.