c.670. Picts rebel against Ecgfrith of Northumbria, but are defeated
This battle is mentioned only in Stephen's Life of Bishop Wilfrid, chapter 19. The Picts are stated to be rebelling against English rule, so Oswiu must have subjected at least some of them. Stephanus dates the rebellion only to Ecgfrith's "early years": it should perhaps be dated to just after Oswiu's death, with the Picts hoping to take advantage of the change of ruler to establish their freedom. Ecgfrith, with the assistance of the sub-king Beornhæth and a troop of horsemen, slew many of the Picts and reduced the rest back to subjection under his rule until his death (fighting the Picts in 685).
Beornhæth is one of the nine named ealdormen after Ecgfrith (and before King Aldfrith) in the list of kings and ealdormen in the Durham Liber Vitae. The next name in the list is that of Berhtred, who died fighting the Picts in 698 and whom the Annals of Tigernach call the son of Beornhæth. Though there is no explicit link, it is tempting to add the Ealdorman Berhtfrith who defeats the Picts in 711 to this family. His name is similar to Berhtred's, and his position to Beornhæth's (Stephanus in chapter 60 calls Beorhtred King Osred's right-hand man, just as Beornhæth was Ecgfrith's sub-king): it may be that three generations of the family held the key role in Northumbria's armies.