The war between Briton and Englishman which had languished since the battle of Chester had been revived some twelve years before by an advance of the West-Saxons to the south-west.

Unable to save the possessions of Wessex north of the Thames from the grasp of Wulfhere, their king, Cenwealh, sought for compensation in an attack on his Welsh neighbours.

A victory at Bradford on the Avon enabled him to overrun the country near Mendip which had till then been held by the Britons; and a second campaign in 658, which ended in a victory on the skirts of the great forest that covered Somerset to the east, settled the West-Saxons as conquerors round the sources of the Parret.

It may have been the example of the West-Saxons which spurred Ecgfrith to a series of attacks upon his British neighbours in the west which widened the bounds of his kingdom.

His reign marks the highest pitch of Northumbrian power.