It must have been with a high degree of confidence, therefore, that, in 825, Beornwulf marched against the West Saxon’s, but was badly defeated at the battle of Ellandun at the hands of their king Egbert, fought at present day Wroughton near Swindon, Wiltshire.
He became king after the death of Beornwulf in battle against the rebellious East Angles, but he too was killed in another failed attempt to subjugate them in the next year.
While the precise period during which the Mercian Supremacy existed remains uncertain (depending upon whether the reigns of Penda and Wulfhere are included), the end of the era is generally agreed to be around 825, following the defeat of King Beornwulf at the Battle of Ellandun, (near the present Swindon).
King Beornwulf was killed fighting the East Anglians in 826, his successor Ludeca suffered the same fate the following year, and Mercia was conquered and occupied by Ecgberht of Wessex in 829.