Hagen im Bremischen belonged to the Prince-Archbishopric of Bremen, established as a territory of imperial immediacy in 1180. The prince-archiepiscopal fortress (Latin: Castrum Hagen, German: Burghagen) dates back to the 12th century, probably Prince-Archbishop Hartwig II initiated its construction. Since the 14th century the fortress became also used as a residential castle by the Bremian prince-archbishops. The present structure was formed between 1502 until latest 1507 by Prince-Archbishop Johann Rode. In the mid-16th century the inhabitants adopted Lutheranism. During the Leaguist occupation under Tilly (1628–1630), they suffered from attempts of reCatholicisation.
The coat of arms shows an oak, which refers to the place's name Hagen, an antiquated word for forest. The oak bears the coat of arms of the Prince-Archbishopric of Bremen, which refers to the second name element im Bremischen, meaning literally in the Bremian (country). The Bremian coat of arms displays two argent (silver) crisscrossed keys on a gules (red) background. The key is the epithet symbol of Simon Petrus, the saint patron of the Bremen Cathedral. A single key is also the main element in the coat of arms of the city state of Bremen (see Coat of arms of Bremen) and of the formerly Bremian city of Stade.