Not all incumbents of the Bremian See were imperially invested princely power as Prince-Archbishops and not all were papally confirmed as bishops.
In 1180 part of the Bremian diocesan territory and small parts of the neighbouring Diocese of Verden were disentangled from the Duchy of Saxony and became an own territory of imperial immediacy called Prince-Archbishopric of Bremen (German: Erzstift Bremen), a vassal of the Holy Roman Empire.
The prince-archbishopric was an elective monarchy, with the monarch being the respective archbishop usually elected by the Bremian Chapters at Bremen Cathedral and Hamburg Concathedral, with the latter enfranchised to three capitular votes, and confirmed by the Holy See, or exceptionally only appointed by the Holy See.
Papally confirmed archbishops were then invested by the emperor with the princely regalia, thus the title prince-archbishop.
A number of incumbents, elected by the chapter, neither achieved papal confirmation nor imperial investiture, but as a matter of fact nevertheless de facto held the princely power.