The first settlements in Regensburg date to the Stone Age. The Celtic name Radasbona was the oldest name given to a settlement near the present city. Around AD 90, the Romans built a fort there.
In 179, the Roman fort Castra Regina ("fortress by the river Regen") was built for Legio III Italica during the reign of Emperor Marcus Aurelius. It was an important camp on the most northern point of the Danube: it corresponds to what is today the core of Regensburg's Altstadt ("Old City") east of the Obere and Untere Bachgasse and West of the Schwanenplatz. It is believed that even in late Roman times the city was the seat of a bishop, and St Boniface re-established the Bishopric of Regensburg in 739.
From the early 6th century, Regensburg was the seat of the Agilolfing ruling family. From about 530 to the first half of the 13th century, it was the capital of Bavaria. Regensburg remained an important city during the reign of Charlemagne. In 792, Regensburg hosted the ecclesiastical section of Charlemagne's General Assembly. The bishops in council condemned the heresy of Adoptionism taught by the Spanish bishops, Elipandus of Toledo and Felix of Urgel. After the partition of the Carolingian Empire, the city became the seat of the Eastern Frankish ruler, Louis II the German in 843. Two years later, fourteen Bohemian princes came to Regensburg to receive baptism there. This was the starting point of Christianization of the Czech people, and the diocese of Regensburg became the mother diocese of Prague. These events had a wide impact on the cultural history of Czech lands, as they were consequently incorporated into the Roman Catholic and not into the Slavic-Orthodox world. The fact is well remembered, and a memorial plate at St John's Church (the alleged place of the baptism) was unveiled a few years ago, commemorating the incident in the Czech and German languages.
In 1096, on the way to the First Crusade, Peter the Hermit led a mob of Crusaders that
