The English ('Anglo-Saxon') kingdom of Northumbria was constructed in the first half of the seventh century AD from two smaller kingdoms, Deira, which was roughly the area of modern Yorkshire, and Bernicia, which was roughly modern Northumberland and County Durham, plus some of Lothian (see map). The name 'Northumbria' is first recorded by Bede, and as Bede has to explain more than once that it means 'the people living north of the River Humber', it seems clear that the name was a fairly new coinage at the time and may have been Bede's invention. Each of the two constituent kingdoms had its own royal dynasty, and the struggles between them are the stuff of sagas.
My attention was drawn to one character in this saga, Eadwine of Deira (585 - 633 AD), who is the central character in my novel Paths of Exile. One aspect that attracted me to start telling his story is that he had endured a long period of exile and not only survived it but returned to build a great kingdom. Now, the first thing I needed to start building Eadwine's story is the dates of his exile. We can deduce from the length of his reign given in Bede's Ecclesiastical History of the English People that his exile ended some time in 617 AD, when he was about 32. But when did it begin?
We know from Bede that Eadwine's deadly enemy was Aethelferth the King of Bernicia, and that Eadwine was a fugitive during Aethelferth's reign. It seems likely, therefore, that Eadwine's exile began when Aethelferth annexed Deira and combined it with his own kingdom of Bernicia to make the larger unit that Bede and later ages called Northumbria. So when did Aethelferth annex Deira?
Bede gives no direct date, but the Ecclesiastical History mentions several snippets that may have bearing on the case:
On the Reckoning of Time, written in 725 AD, provides additional information*:
He [Pope Gregory] sent to Britain Augustine, Mellitus and John, and many others, with God-fearing monks with them, to convert the English to Christ. [ .] However, the people of the Angles north of the river Humber, under Kings Aelle and Aethelfrith, did not at this time hear the Word of life.
--Bede, On the Reckoning of Time, Chapter 66 (4557). Translated by Faith Wallis.
Chapter 63: "Eadfered Flesaurs reigned twelve years in Bernicia, and twelve others in Deira"
Eadfered is an alternative spelling of Aethelferth or Ethelfrid, and Flesaurs is a Brittonic nickname meaning something like 'The Artful' or 'The Twister'. The total of 24 years for the total reign length agrees with Bede.
A.D. 588. This year died King Ella; and Ethelric reigned after him five years.
A.D. 593. This year Ethelfrith succeeded to the kingdom of the Northumbrians. He was the son of Ethelric; Ethelric of Ida.
Aelle (Ella) appears in king-lists as the father of Eadwine
"Aethelferth not only drove from his kingdom Aella king of the Deirans whose daughter he had married, but after inflicting a series of defeats on him and expelling him from several refuges he deprived him of his life and kingdom together."
-Quoted in John Marsden, Northanhymbre Saga.
Historia Brittonum is specific and precise; Aethelferth ruled for a total of 24 years, and was king of Deira for 12 of them. Bede confirms the 24-year total and as we can deduce from his dates that Aethelferth's reign ended in 617 AD, we can further deduce that Aethelferth's reign began in 593 AD and thus that he annexed Deira some time in 605 AD.
This is a year or two after his victory over Dal Riada, and a year or two after his marriage to Acha. Perhaps significantly, it is also after the birth of Oswald, who had Deiran royal blood and thus a claim to the Deiran kingdom through his mother Acha. Perhaps Aethelferth was on a roll after his victory over Dal Riada, and had decided to turn his attention southwards after securing his position in the north. The date also fits with Reginald of Durham's assertion that Aethelferth annexed Deira after his marriage to Acha.
The date even fits with Pope Gregory's encounter with the slave boys, as this occurred between 585 and 590 AD and Aelle would have been king in Deira until 605 AD.
Furthermore, Bede's statement in On the Reckoning of Time that Aelle and Aethelfrith (Aethelferth) were ruling north of the Humber when St Augustine arrived in 597 AD clearly shows that Aelle was king at least until 597 and that Bede believed Aelle and Aethelferth to be contemporaries, not successors.
So we have three different sources, one eighth-century English (Bede's two books, which I count as one source because they were written by the same author), one ninth-century Brittonic (Historia Brittonum) and one medieval English (Reginald of Durham) that don't contradict each other and that are all consistent with a date of 605 AD for Aethelferth's military annexation of Deira and the beginning of Eadwine's exile. Eadwine would have been a young adult at the time, aged about 20. He would have been old enough to be a significant threat to Aethelferth, especially if he was already showing signs of his later prowess as a warrior, and this would explain why Aethelferth hunted him all over Britain for the next dozen years. So this is the date I went with in Paths of Exile, which is set in the autumn and winter of 605 and 606 AD. The Anglo-Saxon Chronicle's date of 588 AD for Aelle's death conflicts with this interpretation, but I think the balance (three sources against one) favours the date of 605 AD. I also think the conflict can be at least partly reconciled (see "Two Aethelrics").
Full-text sources available online are linked in the text.
Bede: The Reckoning of Time. Translated by Faith Wallis. Liverpool University Press, 1999, ISBN 0-85323-693-3.
*My thanks to Doug Tankard for drawing my attention to the reference to Aelle
and Aethelferth in On the Reckoning of Time.