Both these kings were slain by .Ceadwalla in the following year, but shortly afterwards the Welsh king was overthrown by Oswald, brother of Eanfrith, who reunited the whole of Northumbria under his sway and acquired a supremacy analogous to that previously held by Edwin.
It was during his reign in 827 that Northumbria acknowledged the supremacy of Ecgberht, king of Wessex.
His power was no greater than that of Oswio or Off a had been, and the supremacy might perhaps have tarried with Wessex no longer than it had tarried with Northumbria or Mercia if it had not chanced that the Danish raids were now beginning.
Thus Northern Mercia, East Anglia, the greater part of Essex and Northumbria were handed over to the Danes and henceforth constitute the district known as the Danelagh.
The strength of Mercia or Northumbria might be mustered for, a single battle, but could not supply a standing army to hold down the vanquished.
This diversity of usage was ended, so far as the kingdom of Northumbria was concerned, by the council of Streaneshalch, or Whitby, in 654.
It is probable that down to the end of the 7th century, if not still later, the court poets of Northumbria and Mercia continued to celebrate the deeds of Beowulf and of many another hero of ancient days.
He annexed Kent and East Anglia,overawed Northumbria and Wessex, both hopelessly faction-ridden at the time, was treated almost as an equal by the emperor Charles the Great, and died still at the height of his power.
About two years later, however, both these kings were expelled by Edmund, and the whole of Northumbria was brought under his power.
The southern part of Northumbria now passed entirely into the hands of the invaders, but they allowed a certain Ecgberht to reign over the portion of the kingdom north of the Tyne.