[Bæda, Hist. Eccles. lib. iii. cap. 21, 25, 28, lib. v. cap. 20, Vit. Abb. 317; Florence of Worcester; Eddius, in Historians of York, ed. Raine, R.S. i.; J. R. Green, Making of England, c. vii.]
ALCHFRITH (fl. 655) was the son of Oswiu, king of the Northumbrians, and Eanflæd, daughter of Eadwine. When, by the overthrow of Oswini of Deira, Oswiu became king of all Northumbria, he made Alchfrith under-king of the Deirans. Alchfrith married Cyneburh, daughter of Penda, the heathen king of the Mercians. When Peada, the brother of Cyneburh, sought Alchflæd, the sister of Alchfrith, in marriage, Alchfrith brought him to accept christianity, which was the condition of his being allowed to win his bride. In spite of his connection with the royal house of Northumbria, Penda made another fierce incursion into that kingdom. Alchfrith joined his father and met the invaders, in 655, near the river Winwæd. The Mercian host greatly outnumbered the small army of the Northumbrian kings, but it was utterly routed and Penda was slain in the battle. Alchfrith took a prominent part in the struggle between the Celtic and Roman churches. His mother Eanflæd, on the defeat and death of her father, was taken for refuge to Kent, the kingdom of her mother's brother. There she was brought up in the practices of the Roman church. She still adhered to these practices after her return to Northumbria and her marriage to Oswiu, who followed the teaching of the Irish missionaries. Alchfrith at first favoured the Celtic teachers, and at his bidding Eata, the abbot of Melrose, founded the monastery of Ripon, where for a while Cuthbert dwelt. The influence, however, of his mother Eanflæd was strong. She had already sent Wilfrith, who was discontented with Lindiafame, to the court of Kent. Benedict Biscop had already left Northumbria for Rome, and Alchfrith made a vow that he also would make the same pilgrimage. This vow was not fulfilled, but when Wilfrith came back from his visit to Gaul, Alchfrith took him for his teacher and definitely joined the Roman party. He gave Wilfrith the monastery of Ripon, and the new abbot drove Cuthbert and his fellows away. The cause of the dispossessed monks was taken up by Colman, bishop of Lindisfarne. Alchfrith sent for Agilberct, the Frankish bishop of the West Saxons, to help the Roman party, and caused him to ordain his friend Wilfrith priest in the monastery of Ripon. Alchfrith was present at the synod held at Whitby in 664, where Colman and his Irish brethren were defeated by the defection of Oswiu to the Roman party. In the course of the same year Alchfrith, by the advice of his father, sent Wilfrith to Agilberct, who was then bishop of Paris, for episcopal ordination. Alchfrith made war against his father, and probably took refuge in Mercia. The date of his death is not known.