According to the Anglo-Saxon Chronicle, in 789 ‘three ships of the Northmen’ arrived and killed a reeve who came to meet them. In all probability, however, there were earlier raids by Scandinavians which were not recorded in our surviving documentary sources.
Ellis, Caitlin. "The Anglo-Saxon Chronicle records the first Viking raids on England". The Literary Encyclopedia. First published 04 January 2016
[http://www.litencyc.com/php/stopics.php?rec=true&UID=6880, accessed 13 February 2016.]