According to the Anglo-Saxon Chronicle, in 815 King Egbert "ravaged in Cornwall, from east to west". This laconic entry records one of a number of military engagements between the Cornish and West Saxons in this period, which culminated in West Saxon victory over a combined Viking and Cornish force at Hingston Down in 838.
Fenton, Albert. "King Egbert of Wessex conquers Cornwall". The Literary Encyclopedia. First published 06 April 2016
[http://www.litencyc.com/php/stopics.php?rec=true&UID=6908, accessed 30 August 2016.]