Offa of Mercia - East Anglia, Wessex and Northumbria

East Anglia, Wessex and Northumbria

In East Anglia, Beonna probably became king in about 758. Beonna's first coinage predates Offa's own, and implies independence from Mercia. Subsequent East Anglian history is quite obscure, but in 779 Æthelberht II became king, and was independent long enough to issue coins of his own. In 794, according to the Anglo-Saxon Chronicle, "King Offa ordered King Æthelberht's head to be struck off". Offa minted pennies in East Anglia in the early 790s, so it is likely that Æthelberht rebelled against Offa and was beheaded as a result. Accounts of the event have survived in which Aethelberht is killed through the machinations of Offa's wife Cynethryth, but the earliest manuscripts in which these possibly legendary accounts are found date from the eleventh and twelfth centuries, and recent historians do not regard them with confidence. The legend also claims that Æthelberht was killed at Sutton St. Michael and buried four miles (6 km) to the south at Hereford, where his cult flourished, becoming at one time second only to Canterbury as a pilgrimage destination.

To the south of Mercia, Cynewulf came to the throne of Wessex in 757 and recovered much of the border territory that Æthelbald had conquered from the West Saxons. Offa won an important victory over Cynewulf at the Battle of Bensington (in Oxfordshire) in 779, reconquering some of the land along the Thames. No indisputably authentic charters from before this date show Cynewulf in Offa's entourage, and there is no evidence that Offa ever became Cynewulf's overlord. In 786, after the murder of Cynewulf, Offa may have intervened to place Beorhtric on the West Saxon throne. Even if Offa did not assist Beorhtric's claim, it seems likely that Beorhtric to some extent recognised Offa as his overlord shortly thereafter. Offa's currency was used across the West Saxon kingdom, and Beorhtric had his own coins minted only after Offa's death. In 789, Beorhtric married Eadburh, a daughter of Offa; the Chronicle records that the two kings combined to exile Egbert to Francia for "three years", adding that "Beorhtric helped Offa because he had his daughter as his queen". Some historians believe that the Chronicle's "three years" is an error, and should read "thirteen years", which would mean Egbert's exile lasted from 789 to 802, but this reading is disputed. Eadburh is mentioned by Asser, a ninth-century monk who wrote a biography of Alfred the Great: Asser says that Eadburh had "power throughout almost the entire kingdom", and that she "began to behave like a tyrant after the manner of her father". Whatever power she had in Wessex was no doubt connected with her father's overlordship.

If Offa did not gain the advantage in Wessex until defeating Cynewulf in 779, it may be that his successes south of the river were a necessary prerequisite to his interventions in the southeast. In this view, Egbert of Kent's death in about 784 and Cynewulf's death in 786 were the events that allowed Offa to gain control of Kent and bring Beorhtric into his sphere of influence. This version of events also assumes that Offa did not have control of Kent after 764–765, as some historians believe.

Offa's marital alliances extended to Northumbria when his daughter Ælfflæd married Æthelred I of Northumbria at Catterick in 792. However, there is no evidence that Northumbria was ever under Mercian control during Offa's reign.