AETHELFRITH, king of Northumbria, is said to have come to the throne in A.D. 593, being the son of Aethelric (prob ably reigned 568-72). He married Acha, daughter of Ella (Aelle), king of Deira, whom he succeeded, probably in 605, expelling his son Edwin. In 603 he repelled the attack of Aidan, king of the Dalriad Scots, at Daegsastan, defeating him with great loss. Later in his reign, probably in 614, he defeated the Welsh in a great battle at Chester, and massacred the monks at Bangor who were assembled to aid them by their prayers. This war had a strategic importance in the separation of the North Welsh from the Strathclyde Britons. In 617 Aethelfrith was defeated and slain at the river Idle by Raedwald of East Anglia, whom Edwin had persuaded to take up his cause.
See Bede, Chronica Maiora, §53i; Hist. Ecc. (Plummer) i. 34, ii. 2 ; Saxon Chronicle, s.a. 593, 603, 6o5, 616 ; Hist. Brittonum, §157, 63 ; Annales Cambriae, s.a. 613.