Eresburg

The largest of the known Old Saxon refuge castles stood on the Eresberg, a low table hill rising 130 to 150 metres above the Diemel, a tributary of the Weser. The hill was settled well before that: sherds of Michelsberg culture pottery have been picked up on the hill, and excavations near the present collegiate church have revealed traces of ditches, ramparts and posts. Radiocarbon dating places those in the pre-Roman Iron Age, the posts cut from trees datable to between 420 and 370 BC.

Older research took the hill for a border fortress of the Cherusci and the stronghold of Segestes, who was supposed to have held his daughter Thusnelda prisoner here. There are no records supporting that theory.

The site lay in the extreme south of the Saxon Gau of Engern, on the border with the Duchy of Franconia, and that position on the frontier left it repeatedly attacked and hard fought over before the Frankish king Charlemagne conquered it in 772, in the course of the Saxon Wars. He had the Irminsul, one of the chief pagan sanctuaries of the Saxons, destroyed, either on the Eresburg itself or in the vicinity.

The wording of the Royal Frankish Annals for 772 leaves the sanctuary's position open, and the Annales Petaviani record that he "conquered the Eresburg and found the place which is called Ermensul, and set these places on fire" — a plural that has been read as Charlemagne moving on from the castle to the sanctuary. Other accounts place him at the Bullerborn, an intermittent spring near Altenbeken, before he took and destroyed the Irminsul site in the days that followed. The question of where the Irminsul stood may in any case be misleading, since there may have been several of them.

In 779 Charlemagne charged Sturmius, abbot of Fulda, with the mission work of this district and directed him to this place. By 784/785 the king was wintering on the Eresburg himself and had a church built there, probably on the site of the former Saxon temple. Pope Leo III is supposed to have stayed at the Eresburg in 799 on his way to Paderborn.

In 915 a bloody feud was fought at the Eresburg between the Saxon duke Henry, later Henry the Fowler, and the East Frankish king Conrad; Theoderich, bishop of Paderborn, is said to have taken part in the fighting in person. In the same year an invading Hungarian force is recorded as defeating a German army at the Eresburg.

In July 938 an army of Otto I besieged the castle, entered in the records as Heresburg, because the rebel Thankmar, the king's elder half-brother, had entrenched himself there. On 28 July the garrison opened the gates of their own accord, in fear of the strength of the force outside, and were plundered anyway. Thankmar fled into the church of St Peter, consecrated by Pope Leo, and gave himself up by laying his sword on the altar. He was attacked there all the same and stabbed from behind by Maincia, a retainer of his other half-brother Henry. Otto regretted what had happened but left it unavenged, while Thankmar's followers were condemned to the gallows. At the scene of the killing, the collegiate church of the former monastery of Obermarsberg in the borough of Marsberg, a crowned head on one of the pillars still recalls the incident.