Around 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 school), which would make it German‘s oldest gymnasium. But the charter with the date is disputed and could be a forgery.

In 889, it was given merchant, customs, and coinage privileges by King Arnulf of Carinthia. It is first mentioned as a "city" in records in 1147.

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 fortification privileges (Befestigungsrecht). Most of the towers that were part of the medieval fortification are still visible in the city. In 1171, Osnabrück received its own judicial authority

From 1412-1669, Osnabrück was a member of the Hanseatic League, the most important trading trust of its time, as well as a member of the Westphalian Federation of Cities.

From 1487 -1512 the Town Hall (Rathaus) was constructed.

As early as 1521, Lutheran sermons were held in the city, and the Reformation was introduced in 1543 after Luther’s Confession.
However, St. Peter’s Cathedral and the St. John’s Church remained Catholic. This is why the city became neither entirely Protestant nor Catholic.

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

The city passed to the Electorate of Hanover in 1803 during the German Mediatisation (annexation) and then briefly to the Kingdom of Prussia in 1806. It was part of the Kingdom of Westphalia from 1807-1810, after which it passed to the First French Empire. After the Napoleonic Wars, in 1815, it fell to the Kingdom of Hanover. Osnabrück was then annexed by Prussia in 1866 after the Austro-Prussian War and administered within the Province of Hanover. The city became part of the new state of Lower Saxony in 1946 after World War II.

Roman Roots: The Battle of Varus
For nearly four centuries, scholars have debated the actual site of the Battle of Varus, in the year 9. A.D., when Germanic tribes lured Roman legions into an ambush only to mow them down for a long time been subject for debate among scholars.

In 1989, more than 6,000 archaeological finds in the hamlet of Kalkriese near Bramsehe, lying north of Osnabrück, confirmed the location. Evidence shows where, on the northern slope of the Kalkriese mountain, a Roman army was vanquished. Weapons, military equipment, everyday items, human and animal bones and more than 1,300 feet of a manmade earthen wall show signs of an ambush and a massacre.

The Teutoburg Forest Battle is a well-known chapter in European history, and it‘s being researched and investigated further. In the award-winning Osnabrück Country Museum and Park Kalkriese, visitors learn about how the battle in Kalkriese, in front of Osnabrück’s city gates, was fought. An exhibition describes the history and research in the museum building, and there are frequent cultural events such a concerts, lectures and light-and-fireworks displays. The extensive park combines the events of that time with the events of today.