Register: https://dgpt.org/wp-content/uploads/2022/03/Register-Archiv-fuer-Deutsche-Postgeschichte-und-Bezirkshefte-1953-1993-Teil-2.pdf
Behringer: Holy Roman Empire as a Communcation Network: https://perspectivia.net/servlets/MCRFileNodeServlet/pnet_derivate_00004689/behringer_core.pdf