During the early ninth century, the equilibrium which existed between the cultures of the British Isles was disturbed by the onset of a new, seaborne power, the Vikings. The first Viking raids took place in the last decade of the eighth century when Lindisfarne was sacked (793). From then on the peoples of the British Isles as a whole were subjected to increasing pressure. Thanks to their longships, a crucial invention, the Vikings were able to dominate for long periods much of the Irish Sea and the North Sea. A completely new situationwas created, as a consequence of which Viking settlements were established along the coasts of Britain and Ireland as well as neighbouring islands including the Isle of Man, Shetland, Orkney and the Hebrides. Though their political power eventually declined, partly as a consequence of political divisions, the communities which they set up remained ethnically distinctive for centuries. With the coming of the Vikings a new period may be said to have begun in the history of the British Isles, one which marked a sharp breach with the past.

The term ‘Viking’ originated in a term for ‘pirate’, but, as with the Saxons earlier, piracy eventually gave way to colonisation. The Irish Sea from the Hebrides southwards was largely dominated by the Vikings, though it would be a mistake to assume that there was political unity among the various groups. (The Irish distinguished ‘dark strangers’ dubhgaill, from ‘fair strangers’ fionngaill, whence came ‘Fingal’.) During the course of the ninth century, trading posts were established at Dublin, Cork, Waterford and Limerick.