Historical study of the origin and Gunzelins the tribal community with the nobles of Hagen in office Salder, reminders of the men and Meinersen.
The History of Hagen at Elme and at the upper Aller, the nobles of Warberg direct descendants, History of Burghagen and research findings on the coat of arms Community Counts of Schwerin, and the nobles of Warberg.
- Bode, George: Gunzelin Hagen of the first Earl of Schwerin and its origin and home, out of line sources and research on the history of Brunswick, Wolfenbüttel: Julius Zwissler, 1912
- Behrndt, Gottfried: News of descent, Life, Tasks performed and the death of the Most Blessed Lord Field Marshal-Lieutenant Busso von Hagen, Berlin: King, 1735
- Hagen, Thomas Philipp von: