Southwest of Bischofsheim, about halfway to the Kreuzberg mountainruins of the old town can be found on a basalt cone. Osterburga Romanesque fortification. Its name has been the subject of much speculation and even more fabulation. It is likely that the name Osterburg has something to do with the cardinal point. The Bischofsheim Osterburg has often been confused with the Osterburg towering over Henfstädt near Themar. In fact, the two castles have nothing in common apart from the similarity in name.

The remote Osterburg castle, situated high above Bischofsheim, was just like the Walzburg the High medieval administrative center of Würzburg in the Brendtal valley and Kreuzberg area. It was also Border fortress against the Hochstift Fulda and military base in the dispute over the Dammersfeld. The origins of the castle, the reason for its construction, the builder and the time it was built are shrouded in mystery. Its name first appears in documents around 1200, when a Reinhold von Osterburg appears as a documentary witness. Like Salzburg, Bischofsheim Osterburg was a Würzburg Ganerbenburg. Engelbert von Osterburg, Botho von Eberstein and Heinrich von Lure, among others, are named as the heirs.

The Osterburg Ganerben, like a large part of the Buch and Rhön nobility, were in dispute with the Prince-Abbot of Fulda. The cause of the dispute was the reclaiming of property from the monastery of Fulda. In the opinion of the knights, however, the documents to which the monastery referred were forgeries in favor of the abbey. The indignation over this and other unreasonable demands finally culminated in the murder of the Prince-Abbot Bertho II of Leibolz. Bertho's successor restored order with a firm hand in the interests of the High Abbey. The time for this was extremely favorable. It was the time after the interregnum, a time of the law of the jungle and feuding. The result was a great deal of political character assassination. It was worth denouncing unruly nobles as robber barons, seizing their castles and seizing their assets.