The town of Obermarsberg is one of the oldest settled points in the Hochsauerland district. In 772, during his Saxon campaign, Charlemagne conquered Eresburg, the largest Saxon folk castle known to date, and subsequently destroyed the Irminsul, a cult site of the Saxons. In 784/85 Charlemagne wintered in Obermarsberg and had a royal St. Peter's church, a basilica - presumably in the northeast of the castle district - built on the site of an earlier church.
The city was fortified and mostly surrounded by a strong wall with 7 towers. 2 gates closed the town. The people of Obermarsberg were proud of their market privileges. Every year 5 fairs were held.
Thanks to its sights, its tradition and the great view Obermarsberg is a popular place for excursions.