Egbert of Wessex won a decisive victory over Beornwulf of Mercia and proceeded to take control of the Mercian dependencies in southeastern England (Kent, Surrey, Sussex and Essex). East Anglia and Northumbria also acknowledge Egbert as overlord. The Anglo-Saxon Chronicle subsequently described Egbert as a bretwalda, or “Ruler of Britain”.
Editors. "Battle of Ellandun; Wessex becomes the dominant Anglo-Saxon kingdom". The Literary Encyclopedia. First published 01 May 2009
[http://www.litencyc.com/php/stopics.php?rec=true&UID=6917, accessed 29 November 2015.]