Aldfrith (Early Modern Irish: Flann Fína mac Ossu; Latin: Aldfrid, Aldfridus; died 14 December 704 or 705) was king of Northumbria from 685 until his death.

His reign was relatively peaceful, marred only by disputes with Bishop Wilfrid, a major figure in the early Northumbrian church.

However, in 685, when Ecgfrith was killed at the battle of Nechtansmere, Aldfrith was recalled to Northumbria, reportedly from the Hebridean island of Iona, and became king.

In his early-8th-century account of Aldfrith's reign, Bede states that he "ably restored the shattered fortunes of the kingdom, though within smaller boundaries".

[2] His reign saw the creation of works of Hiberno-Saxon art such as the Lindisfarne Gospels and the Codex Amiatinus, and is often seen as the start of Northumbria's golden age.

[4] He became a fluent speaker of Old Irish,[5] and may have married a princess of the Uí Néill dynasty, probably Fín the daughter (or possibly granddaughter) of Colmán Rímid.

[8] Irish law made Fín's kin, the Cenél nEógain of the northern Uí Néill, responsible for his upbringing.

[9] The relationship between Aldfrith's father and mother was not considered a lawful marriage by Northumbrian churchmen of his day, and he is described as the son of a concubine in early sources.

The 8th-century monk and chronicler Bede lists both Oswald and Oswiu as having held imperium, or overlordship, over the other Anglo-Saxon kingdoms; in Oswiu's case his dominance extended beyond the Anglo-Saxons to the Picts, the Gaels of Dál Riata, and the many obscure and nameless native British kingdoms in what are now North West England and southern Scotland.

[11] Oswiu's overlordship was ended in 658 by the rise of Wulfhere of Mercia, but his reign continued until his death in 670, when Ecgfrith, one of his sons by his second wife, Eanflæd, succeeded him.

Ecgfrith was unable to recover Oswiu's position in Mercia and the southern kingdoms, and was defeated by Wulfhere's brother Æthelred in a battle on the River Trent in 679.

[12] Ecgfrith sent an army under his general, Berht, to Ireland in 684 where he ravaged the plain of Brega, destroying churches and taking hostages.

[18][19] Ecgfrith was killed during a campaign against his cousin, the King of the Picts Bridei map Beli, at a battle known as Nechtansmere to the Northumbrians, in Pictish territory north of the Firth of Forth.

[21] Ecgfrith's death threatened to break the hold of the descendants of Æthelfrith on Northumbria, but the scholar Aldfrith became king and the thrones of Bernicia and Deira remained united.

[24] The historian Herman Moisl, for example, wrote that "Aldfrith was in Iona in the year preceding the battle [of Nechtansmere]; immediately afterwards, he was king of Northumbria.

[27] Bede, paraphrasing Virgil, wrote that following Ecgfrith's death, "the hopes and strengths of the English realm began 'to waver and slip backward ever lower'".

[28] Aldfrith ruled both Bernicia and Deira throughout his reign, but the two parts remained distinct, and would again be divided by the Vikings in the late 9th century.

[30] The details of the early Middle Ages in northwest England and southwest Scotland are more obscure, but a Bishop of Whithorn is known from shortly after Aldfrith's reign.

Some archaeological evidence, the Roman Rig dyke, near modern Sheffield, appears to show that it was a defended border, with large earthworks set back from the frontier.

Important monasteries existed at Whitby, where the known abbesses tended to be members of the Deiran royal family, at Monkwearmouth-Jarrow, where Bede was a monk, and at Ripon.

[35] Aldfrith appears to have had the support of leading ecclesiastics, most notably his half-sister Ælfflæd and the highly respected Bishop Cuthbert.

[37] Aldfrith also owned a manuscript on cosmography, which (according to Bede) he purchased from Abbot Ceolfrith of Monkwearmouth-Jarrow in exchange for an estate valued at eight hides.

[40] Bede described Aldfrith as a scholar, and his interest in learning distinguishes him from the earlier Anglo-Saxon warrior kings, such as Penda.

It implies a degree of learning and wisdom that led historian Peter Hunter Blair to compare Aldfrith to the Platonic ideal of the philosopher king.

Wilfrid's hagiographer writes:[47]For a while all would be peace between the wise King Aldfrith and our holy bishop, and a happier state of affairs could hardly be imagined.

In 702 or 703, Aldfrith convened a council at Austerfield, on the southern border of Northumbria, which was attended by Berhtwald, Archbishop of Canterbury, and many bishops.

The period saw the flowering of Insular art in Northumbria and produced the Lindisfarne Gospels, perhaps begun in Aldfrith's time, the scholarship of Bede, and the beginnings of the Anglo-Saxon missions to the continent.