In the early 9th century King Gudfred had made Denmark into an expansive power which threatened the Carolingian positions in Frisia, Saxony and the Slavic lands.

He was, however, challenged by another claimant called Anulo (Ale), who was a grandson or nephew (nepos) of Harald and probably the son of the chief Halfdan who submitted to Charlemagne in 807.

The two rival kings summoned their followers and met in a huge battle which, according to the Frankish annals, cost the lives 10,940 men on both sides.

[3] Adam's Gesta Hammaburgensis Ecclesiae Pontificum was known to some High medieval Norse writers who elaborated on his data.

[4] Various king lists such as the Gesta Danorum of Saxo Grammaticus (c. 1200) combine the names as Sigurd Hring and present this figure as the father and predecessor of the renowned Viking ruler Ragnar Lodbrok, conflated with historical Ragnfred.