The Battle of Clontarf was fought on the 23th April 1014 at Clontarf, near Dublin. The history of early Ireland, Foras Feasa ar Éirinn (literally Foundation of Knowledge on Ireland though often known as The History of Ireland) by Geoffrey Keating gives one of the best known early descriptions of the Battle of Clontarf. A (heavily criticised) 1723 English language translation of the Foras by Dermot O’Connor contains the first printed image of Brian Boru, shown above. The original work was written in Irish.
Apart from its historical interest, the book plays a part in the history of Irish thought. The Feasa is intended not merely to document events but to put forward a particular viewpoint – to defend Ireland against criticisms going back as far as Gerald of Wales, to outline the relationship of Ireland to the English king and define Irish identity.
The work also includes the concept of rule by consent, an idea that became very important in the 17th and 18th centuries [FFÉ, p. 183]:
We do not read in the seanchas that there was ever any king of Ireland from the time of Slainghe to the Norman invasion but a king who obtained the sovereignty of Ireland by the choice of the people, by the excellence of his exploits, and by the strength of his hand.