,
County Durham. The stone churches built for Nechtan, and perhaps Óengus's church at St Andrews, are presumed to have been similar.|alt=Colour photo of an 8th century church In 740, a war between the Picts and the Northumbrians is reported, during which
Æthelbald,
King of Mercia, took advantage of the absence of
Eadberht of Northumbria to ravage his lands, and perhaps burn
York. The reason for the war is unclear, but it has been suggested that it was related to the killing of Earnwine son of
Eadwulf on Eadberht's orders. Earnwine's father had probably been an exile in the north after his defeat in the civil war of 705–706, and it may be that Óengus, or Æthelbald, or both, had tried to place him on the Northumbrian throne. Battles between the Picts and the Britons of Alt Clut, or
Strathclyde, are recorded in 744 and again in 750, when
Kyle was taken from Alt Clut by Eadberht of Northumbria. The
battle of Catohic between the Britons and the Picts is reported at a place named Mocetauc (perhaps
Mugdock near
Milngavie) in which Talorgan mac Fergusa, Óengus's brother, was killed. Following the defeat in 750, the
Annals of Ulster record "the ebbing of the sovereignty of Óengus". This is thought to refer to the coming to power of
Áed Find, son of Eochaid mac Echdach, in all or part of Dál Riata, and his rejection of Óengus's overlordship. A number of interpretations have been offered of the relations between Óengus, Eadberht and Æthelbald in the period from 740 to 750, which due to the paucity of sources remain otherwise unclear. One suggestion is that Óengus and Æthelbald were allied against Eadberht, or even that they exercised a joint rulership of Britain, or , Óengus collecting tribute north of the River Humber and Æthelbald south of the Humber. This rests largely on a confused passage in Symeon of Durham's
Historia Regum Anglorum, and it has more recently been suggested that the interpretation offered by
Frank Stenton — that it is based on a textual error and that Óengus and Æthelbald were not associated in any sort of joint overlordship — is the correct one. In 756, Óengus is found campaigning alongside Eadberht of Northumbria. The campaign is reported as follows: In the year of the Lord's incarnation 756, King Eadberht in the eighteenth year of his reign, and Unust, king of Picts led armies to the town of
Dumbarton. And hence the Britons accepted terms there, on the first day of the month of August. But on the tenth day of the same month perished almost the whole army which he led from Ouania to Niwanbirig. That Ouania is
Govan is now reasonably certain, but the location of Newanbirig is less so. Newburgh-on-Tyne near
Hexham has been suggested. An alternative interpretation of the events of 756 has been advanced: it identifies Newanbirig with
Newborough by
Lichfield in the kingdom of Mercia. A defeat here for Eadberht and Óengus by Æthelbald's Mercians would correspond with the claim in the Saint Andrews foundation legends that a king named Óengus son of Fergus founded the church there as a thanksgiving to
Saint Andrew for saving him after a defeat in Mercia. Marjorie Anderson supports this version of the St Andrews foundation legend. == Cult of Saint Andrew ==