During the seventh century AD, the
Northumbrians gradually extended their territory to the north. The
Annals of Tigernach record a siege of "Etain" in 638, which has been interpreted as Northumbria's conquest of
Eidyn (
Edinburgh) during the reign of
Oswald, marking the annexation of
Gododdin territories to the south of the
River Forth. To the north of the Forth, the Pictish nations consisted at this time of the Kingdom of
Fortriu to the north of the
Mounth, and a "Southern Pictish Zone" between there and the Forth. Evidence from the eighth century Anglo-Saxon historian
Bede points to the Picts also being subjugated by the Northumbrians during Oswald's reign, and suggests that this subjugation continued into the reign of his successor,
Oswiu.
Ecgfrith succeeded Oswiu as king of Northumbria in 670. Soon after, the Picts rose in rebellion against Northumbrian subjugation at the
Battle of Two Rivers, recorded in the 8th century by
Stephen of Ripon,
hagiographer of
Wilfrid. Ecgfrith was aided by a sub-king,
Beornhæth, who may have been a leader of the Southern Picts, and the rebellion ended in disaster for the Northern Picts of
Fortriu. Their king,
Drest mac Donuel, was deposed and was replaced by
Bridei mac Bili. By 679, the Northumbrian hegemony seems to have started to fall apart. The Irish annals record a Mercian victory over Ecgfrith at which Ecgfrith's brother,
Ælfwine of Deira, was killed. Sieges were recorded at
Dunnottar, in the northernmost region of the "Southern Pictish Zone" near
Stonehaven in 680, and at Dundurn in Strathearn in 682. The antagonists in these sieges are not recorded, but the most reasonable interpretation is thought to be that Bridei's forces were the assailants. Bridei is also recorded as having "destroyed" the
Orkney Islands in 681, at a time when the Northumbrian church was undergoing major religious reform. It had followed the traditions of the
Columban church of
Iona until the
Synod of Whitby in 664 at which it pledged loyalty to the Roman Church. The Northumbrian diocese was divided and a number of new
episcopal sees created. One of these was founded at
Abercorn on the south coast of the
Firth of Forth, and
Trumwine was consecrated as Bishop of the Picts. Bridei, who was enthusiastically involved with the church of Iona, is unlikely to have viewed an encroachment of the Northumbrian-sponsored Roman Church favourably. The attacks on the Southern Pictish Zone at Dunnottar and Dundurn represented a major threat to Ecgfrith's
suzerainty. Ecgfrith was contending with other challenges to his overlordship. In June 684, countering a Gaelic-Briton alliance, he sent his armies, led by Berhtred, son of Beornhæth, to
Brega in Ireland. Ecgfrith's force decimated the local population and destroyed many churches, actions which are treated with scorn by Bede. ==Account of the battle==