After Oswio's victory over Penda in 654-655 he annexed the northern part of Mercia to his kingdom and acquired a supremacy over the rest of England similar to that held by his predecessors.
Ecgfrith (q.v.), who succeeded on Oswio's death in 671, expelled the Mercians from Lindsey early in his reign, but was in turn defeated by them in 679, his brother 2Elfwine being slain.
When serving in King Oswio's court, he attracted the notice of the queen, Eanfled, who, fostering his inclination for a religious life, placed him under the care of an old noble, Cudda, now a monk at Lindisfarne.
On his return home, Oswio's son Alchfrid gave him a monastery at Ripon, and, before long, Agilbert, bishop of the Gewissae, or West Saxons, ordained him priest.
During the early part of Oswio's reign the Northumbrian kingdom was repeatedly invaded and ravaged by the Mercians, and on one occasion (before 651) Penda besieged and almost captured the Northumbrian royal castle at Bamborough.