The Anglian territory of Bernicia was approximately equivalent to the modern British counties of Northumberland, Durham, Berwickshire and East Lothian, stretching from the Forth to the Tees. In the early 7th century, it merged with its southern neighbour, Deira, to form the kingdom of Northumbria and its borders subsequently expanded considerably.
This Brythonic kingdom was formed from what had once been the southern lands of the Votadini, possibly as part of the division of a supposed ‘great northern realm’ of Coel Hen in c. AD 420. This northern realm is referred to by Welsh scholars as Yr Hen Ogledd or, literally, "The Old North". The kingdom may have been ruled from the site that later became the English Bamburgh, which certainly features in Welsh sources as Din Guardi. Near this high-status residence lay the island of Lindisfarne (formerly known, in Welsh, as Ynys Metcaut), which became the seat of the Bernician bishops. It is unknown when the Angles finally conquered the whole region, but around 604 is likely.
Some of the Angles of Bernicia (Old English: Beornice) may have been employed as mercenaries along Hadrian's Wall during the late Roman period. Others are thought to have migrated north (by sea) from Deira (O.E: Derenrice or Dere) The first Anglian king of whom we have any record is Ida, who is said to have obtained the throne and the kingdom about 547. His sons spent many years fighting a united force from the surrounding Brythonic kingdoms until their alliance collapsed into civil war.
Ida’s grandson, Æthelfrith (Æðelfriþ), united Deira with his own kingdom by force around the year 604. He ruled the two kingdoms (united as Northumbria) until he was defeated and killed by Rædwald of East Anglia (who had given refuge to Edwin, son of Ælle, king of Deira) around the year 616. Edwin then became king. The early part of Edwin's reign was possibly spent finishing off the remaining resistance coming from Bryneich exiles operating out of Gododdin. After he had defeated the remaining Brythonic population of Bryneich he was then drawn towards similar subjugation of Elmet (a Cumbric speaking territory which once existed in the modern-day West Riding of Yorkshire, near Leeds) which drew him into direct conflict with Wales proper.
Following the disastrous Battle of Hatfield Chase on 12 October, 633, in which Edwin was defeated and killed by Cadwallon ap Cadfan of Gwynedd and Penda of Mercia, Northumbria again was divided into Bernicia and Deira. Bernicia was then briefly ruled by Eanfrith, son of Aethelfrith, but after about a year he went to Cadwallon to sue for peace and was killed. Eanfrith's brother Oswald then raised an army and finally defeated Cadwallon at the Battle of Heavenfield in 634. After this victory, Oswald appears to have been recognised by both Bernicians and Deirans as king of a properly united Northumbria. The kings of Bernicia were thereafter supreme in that kingdom, although Deira had its own sub-kings at times during the reigns of Oswiu and his son Ecgfrith.
Under Deiran rule 616 - 633)