In 851 the Anglo-Saxon Chronicle records a large viking fleet of 350 ships sailing up the Thames and attacking Canterbury and London. Attempted resistance by Brihtwulf, king of the Mercians failed, and he and his army were forced to flee. Following this, the vikings moved into Surrey.
Thomas, Rebecca. "The Danes enter Thames estuary and march on Canterbury". The Literary Encyclopedia. First published 29 February 2016
[http://www.litencyc.com/php/stopics.php?rec=true&UID=6955, accessed 30 April 2016.]