The first recorded landing of Vikings took place in 787 in Dorsetshire, on the south-west coast. The first major attack in Britain was in 793 at Lindisfarne monastery as given by the Anglo-Saxon Chronicle. However, by then the Vikings were almost certainly well-established in Orkney and Shetland, and many other non-recorded raids probably occurred before this. Records do show the first Viking attack on Iona taking place in 794. The arrival of the Vikings (in particular the Danish Great Heathen Army) upset the political and social geography of Britain and Ireland. In 867 Northumbria fell to the Danes; East Anglia fell in 869.

From 865, the Viking attitude towards the British Isles changed, as they began to see it as a place for potential colonisation rather than simply a place to raid. As a result of this, larger armies began arriving on Britain's shores, with the intention of conquering land and constructing settlements there.