Coenwulf (Old English: [ˈkøːnwuɫf]; also spelled Cenwulf, Kenulf, or Kenwulph; Latin: Coenulfus) was the king of Mercia from December 796 until his death in 821.

Eadberht Præn returned from exile in Francia to claim the Kentish throne, and Coenwulf was forced to wait for papal support before he could intervene.

Coenwulf was succeeded by his brother, Ceolwulf; a post-Conquest legend claims that his son Cynehelm was murdered to gain the succession.

Within a decade of his death, the rise of Wessex had begun under King Egbert, and Mercia never recovered its former position of power.

Such a witness list can be seen on the Ismere Diploma, for example, where Æthelric, son of king Oshere of the Hwicce, is described as a "subregulus", or subking, of Æthelbald.

[16] According to the genealogy of Mercian kings preserved in the Anglian collection Coenwulf was descended from a brother of Penda named Cenwealh, of whom there is no other record.

[21] Coenwulf was unwilling to take military action in Kent without acknowledgement from Pope Leo III that Eadberht was a pretender.

[21][27] Leo refused to agree to moving the archiepiscopate to London, but in the same letter he agreed that Eadberht's previous ordination made him ineligible for the throne:[28] And concerning that letter which the most reverend and holy Æthelheard sent to us ... as regards that apostate cleric who mounted to the throne ... we excommunicate and reject him, having regard to the safety of his soul.

[21] The Mercians captured Eadberht, put out his eyes and cut off his hands,[29] and led him in chains to Mercia, where according to later tradition he was imprisoned at Winchcombe, a religious house closely affiliated with Coenwulf's family.

[32] Coenwulf styled himself "King of the Mercians and the Province of Kent" (rex Merciorum atque provincie Cancie) in a charter dated 809.

Sigered appears on two charters of Coenwulf's in 811 as king (rex) of Essex, but his title is reduced thereafter, first to subregulus, or subking, and thereafter to dux or ealdorman.

[41] A civil war in Gwynedd in the 810s ended with the succession of Hywel ap Caradog in 816 or 817, and Coenwulf invaded again, this time ravaging Snowdonia and taking control of Rhufuniog, a small Welsh territory near Rhos.

It is not clear if the Mercians were involved in a battle recorded in Anglesey in 817 or 818, but the following year Coenwulf and his army devastated Dyfed.

The new archdiocese included the sees of Worcester, Hereford, Leicester, Lindsey, Dommoc and Elmham; these were essentially the midland Anglian territories.

[48] Two versions of the events that led to the creation of the new archdiocese appear in the form of an exchange of letters in 798 between Coenwulf and Pope Leo III.

Coenwulf asserted in his letter that Offa wanted the new archdiocese created out of enmity for Jænberht, the Archbishop of Canterbury at the time of the division; but Leo responded that the only reason the papacy agreed to the creation was because of the size of the kingdom of Mercia.

[50] Coenwulf's desire to move the southern archbishopric to London would have been influenced by the situation in Kent, where Archbishop Æthelheard had been forced to flee by Eadberht Præn.

Coenwulf would have wished to retain control over the archiepiscopal seat, and at the time he wrote to the pope Kent was independent of Mercia.

In 808 there was evidently a rift of some kind: a letter from Pope Leo to Charlemagne mentioned that Coenwulf had not yet made peace with Wulfred.

However, Wulfred officiated at the consecration of Coenwulf's brother and heir, Ceolwulf, on 17 September 822, so it is evident that some accommodation had been reached by that time.

[58] A gold coin bearing the name Coenwulf was discovered in 2001 at Biggleswade in Bedfordshire, England, on a footpath beside the River Ivel.

[70] Coenwulf died in 821 at Basingwerk near Holywell, Flintshire, probably while making preparations for a campaign against the Welsh that took place under his brother and successor, Ceolwulf, the following year.

A mid-11th-century source asserts that Cynehelm briefly succeeded to the throne while still a child and was then murdered by his tutor Æscberht at the behest of Cwoenthryth.

This version of events "bristles with historical problems", according to one historian, and it is also possible that Cynehelm is to be identified with an ealdorman who is found witnessing charters earlier in Coenwulf's reign, and who appears to have died by about 812.

[69][73] The opinion of historians is not unanimous on this point: Simon Keynes has suggested that the ealdorman is unlikely to be the same person as the prince and that Cynehelm therefore may well have survived to the end of his father's reign.

[42] Coenwulf was the last of a series of Mercian kings, beginning with Penda in the early 7th century, to exercise dominance over most or all of southern England.

In the years after his death, Mercia's position weakened, and the battle of Ellendun in 825 firmly established Egbert of Wessex as the dominant king south of the Humber.