Everything we know about Degsastan can be written on half a side of paper, if that. According to Bede's Ecclesiastical History, the king of 'the Scots in Britain' (the Dál Riada), Áedán mac Gabráin, became alarmed at the victorious wars and conquests of Æthelfrith, king of Bernicia (the northern of the two Northumbrian kingdoms), and led an army against him. Æthelfrith, however, defeated (and killed almost all of) the Scottish army at a place called 'Degsa's Stone'. So devastating was the battle, said Bede, that since then no king of the Scots had dared to attack the Northumbrians again. However, Theodbald, Æthelfrith's brother, was killed "with all his army". The Anglo-Saxon Chronicle added that "Hering son of Hussa led the army thither". Hussa was, according to king-lists, Æthelfrith's precursor possibly a brother, possibly not. It is not clear if Theodbald fought for or had taken up arms against Æthelfrith. Equally unhelpfully, the Chronicle doesn't specify which army Hering was leading: the English, on Æthelfrith's behalf, or the Scots, in an attempt to seize the Bernician throne!
The late seventh-century life of the Irish saint Columba says that one of Áedán's tell us that a certain Máel Umai fought in a "battle of the Saxons by Áedán" (surely Degsastan) and slew Æthelfrith's brother Eanfrith. Máel Umai was a brother of King Colmán of the Northern Uí Néill (one of the most important Irish kingdoms, whose ruler had a claim to the title of High King), based in what is now Co. Tyrone. However, while Æthelfrith had a called Eanfrith (briefly king in 634), he had no brother of that name that we know of. It's possible, therefore, that this was an error for Theodbald and would support the notion that Theodbald was fighting rather than his brother … assuming of course that Máel was fighting on Áedán's side!
