The town belongs to the (historical) region of Holstein, today in the German state of Schleswig-Holstein.

Oldenburg was the chief town of the Wagrians, one of the Slavic peoples that migrated as far west as the river Elbe in or after the 6th century (see Völkerwanderung), also known as Wends and Obotrites.

Emperor Otto I established the bishopric of Oldenburg under Adaldag, archbishop of Hamburg.

To the Northern Germanic Vikings, the city was known as Brandehuse, i.e. "the burned houses", indicating the bellicose times.

For centuries, Starigard/Oldenburg remained the Slavic competitor of Hedeby on the Baltic trade, until the counts Adolph I and Adolph II of Schauenburg and Holstein, supported by Henry the Lion, finally defeated the Wends during the first half of the 12th century.