Under Adaldag the metropolitan see obtained its first suffragans, by the erection of the bishoprics of Ribe, Schleswig, and Århus; and that of the Slavic territories of Aldenburg (today's Oldenburg in Holstein) was also placed under Hamburg.
The original diocese was founded about 970 by Emperor Otto I in the Billung March at Oldenburg in Holstein (Aldinborg or Starigard), the former capital of the pagan Wagri tribe.
He was a friend of the two bishops of Oldenburg in Holstein, Vicelinus (died 1154) and Gerold (died 1163), who did much to Christianize the Polabian Slavs.
In 1173 Henry the Lion founded the cathedral to serve the Diocese of Lübeck, after the transfer in 1160 of the bishop's seat from Oldenburg in Holstein under bishop Gerold.
Wagria Castle occupied a central location in Oldenburg in Holstein (then called Starigard, or "Old Castle"); its ramparts still exist.
Waldemar Magunia (born December 8, 1902 in Königsberg (Prussia) - died February 16, 1974 in Oldenburg in Holstein) was the leader of the Sturmabteilung (SA) in East Prussia and Commissioner General in Kiev.
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