At the beginning of the Viking age the great emperor Charlemagne ruled south of Denmark. He had forced nation after nation to submit to his rule. The ‘Abodrites’ and ‘Frisians’ had become his allies and in 776 only the Saxons were left.
They lived just south of Denmark and sought the help of the Danes. The Danish king Godfred put up a furious resistance to the Franks. We don’t know how large Godfred’s kingdom was but he was a strong king. When he met the Frankish forces at the border town of Sliestorp with his fleet and all of his cavalry they decided to deal instead of figh Godfred later threatened to attack Charlemagne’s allies and the Franks’ capital at Aachen with a large army.
Charlemagne died in 814 but his successor Ludwig pushed into Jutland in 815. He was however repulsed, surely by Danish knights from the ‘ringborge’ (Ring Castle, castle formed as a circle). After this the Franks tried to gain influence with the Danes through Christianity. The sword was swapped for the cross.