Bede lists Oswiu as the seventh and…
659 CE
Bede lists Oswiu as the seventh and last king to hold imperium (or bretwalda in the language of the Anglo-Saxon Chronicle) over the other Anglo-Saxon kingdoms.
Overlordship is a common relationship between kingdoms at this time, often taking the form of a lesser king under the domination of a stronger one.
Oswiu had gone further than this, however, and had installed his own governors in Mercia after the deaths of Penda and Peada.
This attempt to establish close control of Mercia fails in 658 when three Mercian leaders, Immin, Eafa and Eadbert, rebel against the Northumbrians.
Bede reports that they had kept Wulfhere in hiding, and when the revolt succeeded Wulfhere became king.
It has been suggested that the Mercian revolt succeeded because Oswiu may have been occupied with fighting in Pictland, in northern Britain.
His nephew the Pictish king Talorgan, son of Eanfrith, had died in 657.