Dates: Summer 825

In 823, Beornwulf became King of Mercia after deposing Ceolwulf I. Ceolwulf himself had only been king since 821, suceeding his brother Cœnwulf who died at at Basingwerk near Holywell, Flintshire whilst probably preparing for a campaign against the Welsh at Powys.
Mercia had been the powerhouse of the Anglo-Saxon kingdoms since the age of Penda more than 170 years earlier

In 822 the Mercians, probably under the leadership of Ceolwulf completed what Cœnwulf was likely planning by attacking the Welsh at Deganwy, destroying the fortress at the mouth of the Conway in an attack that preceeded the exile of the last of the ancient Kings of Powys. It was around this time, possibly shortly after this date that Ceolwulf was deposed by Beornwulf.

There is little known about Beornwulf or his family, though his authority was known to have been recognised in Middlesex, Essex and Kent. His father was Ealdorman Beorhtweald, and a man named Beornwulf witnessed charters of King Cœnwulf and King Ceolwulf in 812 and 823, but the position of his name on the charter indicates that this Beornwulf, if the later to be King, was not of a high rank.

During the preceeding fifty or so years, Wessex had suffered with a series of weak kings. The Mercians had asserted dominance, with the borders of Mercia stretching into southern kingdoms such as Kent. Wessex was described by commentators at the time as nothing more than an outlying province. The King of Wessex at the time of Beornwulf's ascendancy was Ecgbehrt. Ecgbehrt himself had been exiled to Gaul in 789 when Beorhtric, his rival, married the daughter of Offa of Mercia. Beorhtric's reign as King of Wessex was one of dependancy on Mercia, and upon his death in 802, the returned Ecgbehrt came to the throne of Wessex. This was opposed by the Mercians, the Hwicce in particular, who, under the command of their Ealdorman, Æþelmund, fought the Wessex men of Wiltshire under Ecgbehrt's brother-in-law Weohstan. The Hwicce were defeated, but both Æþelmund of Mercia and Weohstan of Wessex were killed.
There is nothing written about further clashes between Mercia and Wessex (though there were likely small skirmishes) until 825. The Winchester Chronicles tell us that a challenge had been agreed between Beornwulf of Mercia and King Ecgberht of Wessex. Beornwulf set about raising an army to attack Wessex, the most likely reason territorial gain and to assert his dominance. Ecgberht had been attacking the West Welsh in Dumnonia (modern day Cornwall) in both 815 and 825. He returned home when learning of the Mercian threat to his north border, and had been building his military force with the intention of reinforcing his rule and expanding his Kingdoms borders.

It was in the hot summer of 825 that the Mercians and Wessex met at Ellendun - the exact site of the battle is not known, but is believed to be either Wroughton, south of Swindon, or Lydiard Tregoze, west of the same place. The Mercians, who, it is reported, greatly outnumbered the forces of Wessex, had their southern advance blocked. The two armies lined up on opposite ridges to each other. Ecgberht, upon seeing the larger Mercian force, held council with his thegns to decide whether to cede land to Beornwulf, but his thegns made the decision to battle and defend their border. A bloody battle ensued, the men of Wessex attacked the Mercian line. It was a long and fierce battle, and eventually, Beornwulf's morale broke and is reported to have fled, handing the victory to Wessex.

From this date forwards, the power of Mercia waned and faded. Mercia was never again to trouble Wessex on a mentionable scale. One by one during the coming months and years, areas of Mercian control changed alliegence to Wessex. The age of West Saxon power had begun. After winning the battle, Ecgberht's son, Æþelwulf, the bishop of Sherbourne & Ealdorman of Hampshire was sent to Kent with a large army to expand Wessex borders there - Baldred, who was ruling under Mercia, fled beyond the Thames, and soon Essex, Sussex and Surrey along with Kent submitted to Ecgberht. Beornwulf was killed later in 825 by the East Angles, probably during an attempt to strengthen control there. Just four years later, after a large campaign by Ecgberht, Mercia was under the control of Wessex.

Copyright: 2009 Penda of Teotta's Halh AKA N. Hodgkiss. Reference wikipedia.org & Anglo-Saxon England by Frank Stenton