An entry under the year 839 in the Annals of Ulster (AU) begins with these words:
bellum re genntib for firu fortrenn
‘A battle by the Gentiles against the men of Fortriu’
The Irish annalists used ‘Gentiles’ (i.e. ‘heathens’) as a blanket term for Vikings, regardless of whether they were Norsemen or Danes. We are therefore unable to identify the group of ‘heathens’ referred to here. Their opponents, however, are identifiable as Picts from Fortriu, a region now regarded by historians as broadly coterminous with Moray. The AU entry continues by naming three prominent casualties of the battle:
‘and in it fell Eoganan, son of Oengus, and Bran, son of Oengus, and Aed, son of Boanta; and others fell, almost without number.’
Eoganan (or ‘Ewan’) succeeded to the paramount kingship or overkingship of the Picts in c.836. His father Oengus had ruled from 820 to 834, succeeding his own brother Constantine (also known as ‘Custantin’ or ‘Causantin’), the king commemorated on the magnificent Dupplin Cross. Bran was presumably Eoganan’s brother. Aed, Boanta’s son, was paramount king of the Scots, ruling from a power-base in Argyll. His participation in the battle of 839, fighting alongside the Picts, suggests that he was an ally or vassal of Eoganan. This is consistent with the views of modern historians who envisage a longstanding Pictish dominance of the Scots reaching back to c.790. Oaths of fealty to his Pictish overlord would have required Aed to render military service whenever the need arose, even if it meant a long eastward march to fight a Viking army in Fortriu.
We do not know where the battle of 839 took place. Given the mention of warriors from Moray a location there seems likely but we should also allow the possibility that Eoganan led an army from Fortriu to a battlefield further south in Perthshire. Any Pictish territory would in fact be a candidate. Of one thing we can, at least, be fairly sure: the battle was a catastrophe for Picts and Scots alike. At a single stroke, both peoples were deprived of their kings, both kingdoms now lay at the mercy of the victors. No doubt the triumphant Vikings immediately went on a rampage, plundering the lands of the Picts and sending raiding-parties westward to harrass the Scots. In the ensuing chaos several ambitious figures claimed the vacant Pictish overkingship, among them a certain Cinaed mac Ailpin whose origins are shrouded in mystery. After vanquishing his rivals Cinaed established a new royal dynasty which eventually brought the Picts and Scots together as one people.
It is hard to see how Cinaed could have made his mark on posterity if Eoganan had defeated the Vikings in 839. Medieval Scottish history might have turned out very differently if the men of Fortriu had tasted victory on that fateful battlefield. The slaughter of the Picts and their allies is sometimes called ‘the disaster of 839’, an apt description of an encounter whose political consequences were indeed far-reaching. Alex Woolf suggests that it ‘may be one of the most decisive and important battles in British history’, an observation which surely ranks the disaster of 839 alongside two other famous ‘lost’ battles: Degsastan (603) and Brunanburh (937). All three were events of great significance in their own time, all three were turning-points in the early history of Scotland, but their precise geographical contexts unfortunately elude us.
Alan Orr Anderson, Early sources of Scottish history, AD 500 to 1286. vol.1 (Edinburgh, 1922), p.268 [for the translation of AU 839 used here]
Alex Woolf, From Pictland to Alba, 789-1070 (Edinburgh, 2007), p.66