The Great Heathen Army
In 865, the Great Heathen Army—pagan Norsemen—invaded Christian Anglo-Saxon England. Within five years, three of the four Anglo-Saxon Kingdoms of England had been conquered and in 870, the Great Heathen army attacked the last Kingdom: Wessex, ruled by Alfred the Great.
The Great Heathen Army were mostly Danes, some other Scandinavians, and were pagan (hence the name). They were different from other Viking raids at the time: because the Great Heathen Army stayed in England and established their own kingdoms, replacing the local culture. Archaeology is not ambiguous: the Great Heathen Army was a real thing.
The invasion is recorded in two primary sources: the Anglo-Saxon Chronicle, the oldest version of which we have dates from about the end of King Alfred’s reign (so after the invasion). And the Ragnarssona þáttr, the Saga of Ragnar Lothbrok and his sons, which is a Norse history covering the same subject (partly). Personalities and characters who come up are also recorded in other (mostly Christian) records from the same time… in Germany, Ireland, etc.
Who led the great Heathen Army?
The sources aren’t clear: Ivar the Boneless is attested to in both versions, a commander called Ubba, and third who is called Hvitserk by the Norse, and Halfdan by the Anglo Saxons (Some suggest that this is the same person, the Norse are recording his nickname). The Norse also claim that Bjorn Ironside, the first king of Sweden was involved in the army, but the Anglo-Saxons don’t.
Who were these men?
Well, to the Norse saga, the story is that the commanders of the Great Heathen Army were brothers: Hvitserk, Bjorn, Ubba and Ivar. They were said to be the sons of Ragnar Lothbrok, a great king of all of Scandinavia, who was captured and killed by King Aella of Northumbria, and so the sons of Ragnar invaded (and conquered) England to avenge his death.
The Anglo-Saxons don’t mention a motive for the invasion, the Great Heathen Army suddenly invades, and starts killing Kings and upsetting the existing order. They do mention that Halfdan and Ivar had a brother who was a commander (and it’s inferred to be Ubba)
Ragnar Lothbrok is not supported as having existed historically. No contemporary histories in, or near, Scandinavia record him or his kingdom. And, his saga involves a lot legendary beasts, wives descended from divine beings. What we would happily view as total fiction.
But… we have his sons appearing and doing things in historical records we accept as reliable records, backed up by archaeology. So… is Ragnar inspired fiction? It becomes murky. And it’s all 1000+ years ago. We have our wits alone to guide us in figuring out “what actually happened?”
So: When historic records blend the fantastic (Ragnar Lothbrok was king of all Scandinavia! His first wife was a daughter of Brunhilda!) and the demonstrated (The Great Heathen Army invaded England, and was commanded by three, possibly four men, who are described as “the sons of Ragnar Lothbrok”), and have what’s reasonable reference what’s impossible, a reasonable way to sort it all out?