Northumbria is primarily the name of a petty kingdom of Angles, Danes and Norwegians which was formed in Great Britain at the beginning of the 7th century, and of the much smaller earldom which succeeded the kingdom. The name reflects that of the southern limit to the kingdom's territory, which was the River Humber, and in the 12th century writings of Henry of Huntingdon the kingdom was defined as one of the Heptarchy of Anglo-Saxon kingdoms.

At its greatest the kingdom extended from the Humber to the Forth. The later earldom was bounded by the River Tees in the south and the River Tweed in the north (broadly similar to the modern North East England) and was recognised as part of England by the Anglo-Scottish Treaty of York in 1237. Berwick-upon-Tweed, which is north of the Tweed, was defined as subject to the laws of England by the Wales and Berwick Act of 1746. The land once covered at Northumbria's peak is administered now in divided parts as North East England (Anglian Bernicia), Yorkshire and the Humber (Danish Deira), North West England (Celtic Cumbria), the Scottish Borders, West Lothian, Edinburgh, Midlothian and East Lothian.

Northumbria was originally composed of the union of two independent kingdoms, Bernicia and Deira. Bernicia covered lands north of the Tees, whilst Deira corresponded roughly to modern-day Yorkshire. Bernicia and Deira were first united by Aethelfrith, a king of Bernicia who conquered Deira around the year 604. He was defeated and killed around the year 616 in battle at the River Idle by Raedwald of East Anglia, who installed Edwin, the son of Aella, a former king of Deira, as king.

Edwin, who accepted Christianity in 627, soon grew to become the most powerful king in England: he was recognized as Bretwalda and conquered Rheged, the Isle of Man and Gwynedd in northern Wales. He was, however, himself defeated by an alliance of the exiled king of Gwynedd, Cadwallon ap Cadfan and Penda, king of Mercia, at the Battle of Hatfield Chase in 633.

King Oswald

After Edwin's death, Northumbria was split between Bernicia, where Eanfrith, a son of Aethelfrith, took power, and Deira, where a cousin of Edwin, Osric, became king. Cumbria tended to remain a country frontier with the Britons. Both of these rulers were killed during the year that followed, as Cadwallon continued his devastating invasion of Northumbria. After the murder of Eanfrith, his brother, Oswald, backed by a force of Scots sent by Domnal of Dalriada, defeated and killed Cadwallon at the Battle of Heavenfield in 634.

King Oswald re-introduced Christianity to the Kingdom, but this time, by appointing St Aidan, an Irish monk from the Scottish island of Iona to convert his people. This led to the introduction of Celtic Christianity, as opposed to Roman Catholicism. A monastery was established on Lindisfarne, probably as an echo of the island monastery of Iona.

War with Mercia continued, however. In 642, Oswald was killed by the Mercians under Penda at the Battle of Maserfield. In 655, Penda launched a massive invasion of Northumbria, aided by the sub-king of Deira, Aethelwald, but suffered a crushing defeat at the hands of an inferior force under Oswiu, Oswald's successor, at the Battle of Winwaed. This battle marked a major turning point in Northumbrian fortunes: Penda died in the battle, and Oswiu gained supremacy over Mercia, making himself the most powerful king in England.

Religious Union and the Loss of Mercia

In the year 664 a great synod was held at Whitby to discuss the controversy regarding the timing of the Easter festival. Much dispute had arisen between the practices of the Celtic church in Northumbria and the beliefs of the Roman church. Eventually, Northumbria was persuaded to move to the Roman faith, the Celtic Bishop Colman of Lindisfarne returned to Iona.

Northumbria lost control of Mercia in the late 650s, after a successful revolt under Penda's son Wulfhere, but it retained its dominant position until it suffered a disastrous defeat at the hands of the Picts at the Battle of Nechtansmere in 685; Northumbria's king, Ecgfrith (son of Oswiu), was killed, and its power in the north was gravely weakened. The peaceful reign of Aldfrith, Ecgfrith's half-brother and successor, did something to limit the damage done, but it is from this point that Northumbria's power began to decline, and chronic instability followed Aldfrith's death in 704.

The kingdom's rise and fall

The kingdom was famed as a centre of religious learning and arts. Initially the Northumbria was Christianised by monks from the Celtic Church, and this led to a flowering of monastic life, with a unique style of religious art that combined Anglo-Saxon and Celtic. After the Synod of Whitby in 664 the Celtic and Catholic Churches united. However the unique style was preserved, with its most famous example being the Lindisfarne Gospels. Northumbria became the northern kingdom of the Danelaw, run by Scandinavians who were more or less dependent upon Anglian underlings. Power was even higher under the Danes and Norwegians, who were able to demolish the Kingdom of Strathclyde in right of Northumbria, also annexing the Five Burghs, Isle of Man and Kingdom of Mide in Ireland. Vikings made Northumbria rather wealthy after pillaging it first, with a lucrative trade at Jórvík that extended to the farthest reaches of Europe.

Scots invasions further reduced Northumbria to an earldom stretching from the Humber to the Tweed, and Northumbria was for a long time in territory where sovereignty was disputed between the emerging kingdoms of England and Scotland. The Earls of Northumbria maintained a degree of independence from both, but there were lengthy periods of fighting over control of the earldom.

(Adopted from Wikipedia, EN)