Rudolf appeared to be vulnerable after losing the support of some of the Saxon princes.

Rudolf sought out Henry and met him at Flachheim between Eisenach and Mühlhausen in Thuringia.

Rather than attack Rudolf and possibly get caught with his forces straddling the stream, Henry opted to march around the obstacle.

Henry struck Rudolf's army from the rear, but with ensuing snowstorm the attack became disorganized.

[1] On the other hand, Ekkehard of Aura reports that Otto of Nordheim attacked and plundered Henry's camp before forcing the surrender of the Franconians and the Bohemians.