Who was King Offa of Mercia and what did he do?

Offa of Mercia came to the throne following a period of civil unrest and became arguably the most influential of all Anglo-Saxon kings prior to Alfred the Great. He fought wars, was respected by Frankish king Charlemagne, and constructed one of the great building projects of his age. Here is the remarkable story of King Offa of Mercia.

History Rulers
20 April 2023

Offa of Mercia was a formidable and enigmatic Anglo-Saxon king whose impact has echoed through time, shaping the destinies of future rulers like Alfred the Great and leaving an indelible mark on England’s early history.

Here is the intriguing tale of Offa, Anglo-Saxon king of Mercia as well as the story of the remarkable construction of Offa’s Dyke.

Sources on the Life of King Offa

Dipiction of 'The Lives of the two Offas' (Photo: Culture Club via Getty Images)

Much of the history of seventh and eighth century England and its rulers is shrouded in mystery and conjecture.

No contemporary biography of Offa Rex, King of the Mercians, has survived. Indeed, much of what we are told comes from a number of later sources. Most notably the Anglo-Saxon Chronicle written between the ninth and twelfth centuries. In addition, historians have used Offa’s charters, letters and significant archaeological finds to piece together his life.

The Early Years of King Offa

Offa's Dyke Path and the Jubilee Monument (Photo: Loop Images via Getty Images)

Offa is believed to have been the son of Thingfrith and descended from Eowa, a brother of Penda, who was king of Mercia in the early seventh century. His birth year is unrecorded but it’s likely he was born in the 720s or 730s.

When his distant relative Æthelbald was killed in 757, a power struggle ensued between Offa and a little-known king called Beornred. According to the Anglo-Saxon Chronicle, ‘Beornred succeeded to the kingdom, and held it a little while and unhappily; and that same year Offa put Beornred to flight and succeeded to the kingdom’.

After he ascended to the throne, Offa of Mercia spent the initial period of his kingship consolidating his position within his own kingdom. Once his power base was secured, it was time to look further afield.

Offa the Ambitious

Old map of England, showing the Anglo-Saxon Kingdoms (Photo: mikroman6 via Getty Images)

Eager to expand his realm, Offa’s forces moved on Sussex and Kent, possibly fighting battles near Hastings in 771 and at Otford five years later. However, the extent and duration of King Offa’s control over these kingdoms remain uncertain due to limited historical records from the time.

In 779, he defeated Cynewulf, king of Wessex, and to extend his sphere of influence even further, he arranged for his daughters to marry kings from other kingdoms, including Northumbria. He even offered a son and a daughter to Charlemagne, king of the Franks.

Determined to broaden his realm, Offa set his sights on the neighbouring kingdoms of Sussex and Kent. His forces embarked on military campaigns, engaging in notable battles near Hastings in 771 and another at Otford in 776. Despite these endeavours, the full extent and duration of King Offa’s dominion over these territories remain shrouded in uncertainty, owing to scarce historical records from the period.

When seizing new territory, Offa initiated a departure from tradition by overthrowing and downgrading the status of kings within the lands he conquered, rather than allowing them to continue ruling as subordinate monarchs.

Offa’s ambitions extended beyond Sussex and Kent, as he targeted Wessex in 779, where he achieved a decisive victory over King Cynewulf at the Battle of Bensington. This triumph significantly bolstered Offa’s supremacy over Wessex, allowing him to exert authority and control over the neighbouring kingdom, thereby expanding Mercian influence. Although Offa’s military might was insufficient to conquer Wessex, he adeptly complemented his military success with diplomatic overtures. By arranging the marriage of his daughter Eadburh to Beorhtric, Cynewulf’s successor, Offa secured a valuable alliance to reinforce his military prowess.

Keen to expand his influence further, Offa employed further political influence beyond his borders. He forged further alliances by arranging marriages for his other daughters with kings of other realms, including Northumbria. In a bid to strengthen ties with the powerful Frankish kingdom, Offa even sought a marriage alliance with Charlemagne, the renowned king of the Franks – though the two men fell out over the details of such a proposal.

Offa of Mercia & the Church

Offa's Dyke path sign written in English and Welsh (Photo: Loop Images via Getty Images)

One of the standout aspects of Offa’s reign was his relationship with the church. Through minor incidents around property and grants, he came into conflict with Jænberht, the Archbishop of Canterbury, which became an ongoing problem for Offa.

However, the Mercian King had a good relationship with Pope Adrian I, to whom Offa allowed a certain amount of control over English ecclesiastical matters in return for the creation of a rival archbishopric in Lichfield (which was abolished by 803). This was specifically to free Mercia from the religious authority of Canterbury in the kingdom of Kent, one of his arch enemies.

Offa’s Dyke & the Welsh

Offa's Dyke Footpath passes by a Welsh Hill Farm (Photo: AlasdairJames via Getty Images)

Offa’s Mercian kingdom had frequent run-ins with the Welsh and in the tenth century text Annales Cambriae, it is said he battled against them in 778, 794 and 796.

Possibly built for defence, to demarcate the boundary between England and Wales or to demonstrate Mercian power and ability, Offa’s Dyke is a 285 kilometre (177 mile) earthwork with a deep ditch on the west side. It roughly runs down the border of the two countries and offers unbroken views from Mercia into Wales.

While most sources attribute the building of the dyke to King Offa, radioactive carbon dating suggests it may have been started between the end of Roman rule and the beginning of Anglo-Saxon England sometime in the fifth century.

Money & Stature

Medieval Anglo-Saxon silver Penny of Offa King of Mercia (Photo: Hein Nouwens via Getty Images)

One of the most enduring legacies of the reign of Offa, Anglo-Saxon king of Mercia was his reforms of the system of coinage.

Taking his cue from the French coins of the Carolingian dynasty, Offa’s coins were beautifully and intricately designed and carried the king’s name and, for the first time, that of the moneyer, the man from whose mint the coins emanated.

Indeed it was said that his coins displayed ‘a delicacy of execution which is unique in the whole history of the Anglo-Saxon coinage.’ One stand out aspect of his coins was that his wife Cynethryth was also featured upon them, becoming the only Anglo-Saxon queen to have her name depicted on coinage.

On his charters, Offa usually used the title rex Merciorium – King of the Mercians – but some, whose authenticity are dubious and may be tenth century forgeries, use rex Anglorum, or King of the English. His domination did cover much of the country and it’s possible he did think of himself as such.

Death & Legacy

Saxon cross (Photo: fotoMonkee via Getty Images)

King Offa died in July 796 and was buried at Bedeford, although it’s unclear whether that refers to modern-day Bedford, the county town of Bedfordshire.

He was described by Alfred the Great’s biographer and ninth-century monk Asser as ‘a vigorous king who terrified all the neighbouring kings and provinces around him’.

According to a number of historians, Offa Rex, King of the Mercians, was driven by power and personal ambition rather than any great sense of nation building, but there is no doubt that he was one of the most important of the Anglo-Saxon kings.


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