[1] Since the days of King Offa the Eider river had been the border between the settlement area of the Angles and Saxons.
After Charlemagne had subjected the Duchy of Saxony to his rule, Hemming's predecessor and uncle Gudfred took the chance, crossed the Eider and campaigned in the southern lands, which Charles had left to the allied Obotrites.
The king however was killed by his retinue in 810 and Hemming, to assure his rule against his rivaling cousins, sought peace with the Franks.
His and the Emperor's negotiators met on an island of the Eider in present-day Rendsburg and defined the limits of their spheres of influence.
Though in the following decades several quarrels occurred in the border area and the German King Henry I conquered Danish Hedeby at the Danevirke in 934, the border was confirmed by Canute the Great and King Conrad II in 1025 at the betrothal of their children Gunhilda and Henry III.