How Did Mercia Become One of the Most Powerful Kingdoms of Anglo-Saxon England?

Annie Whitehead

Middle Ages
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For much of the Anglo-Saxon period of English history, the land was dominated by the Midlands kingdom of Mercia. Indeed, some of the most well-known characters lived there: Penda, Offa, Æthelflæd Lady of the Mercians, Lady Godiva, and Eadric Streona.

The Mercians, though, had an inauspicious start. It’s not known exactly where they came from, nor if they even called themselves Mercians. Their ascendancy to power is detailed here.

The border people

The Mercians were, perhaps more than any of the other major kingdoms, a federation rather than a kingdom.

Their name comes from the Old English Myrcne, or Mierce, meaning marcher, or border people, suggesting that it was imposed from elsewhere. The border referred to could have been the one shared with their northern neighbour and almost perpetual enemy, Northumbria, which was also expanding into erstwhile smaller kingdoms and pushing ever further south.

Unfortunately for the Mercian reputation, it is also from Northumbria that we get most of the early information about them. They had a bad press, which is not surprising, given that one of their earliest kings went up against, and killed, Oswald of Northumbria whom Bede idolised.

Bede spoke of the Mercians as living either side of the River Trent, so it is safe to assume that this was their initial power base. In 626 Penda, the famous pagan warrior king, fought the West Saxons at Cirencester and either liberated, or took control of, the Gloucestershire kingdom of the Hwicce.

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Penda

Another smaller kingdom which he seems to have controlled is the Worcestershire kingdom of the Magonsæte. Bringing together these and other smaller realms, which eventually became subkingdoms of Mercia, meant that the Mercians had vast numbers of troops at their disposal. When Penda rode against the Northumbrians at Winwæd in 655, it was said that he had with him ‘thirty duces’.

His army also included the king of East Anglia, and several British princes. Whether they were coerced, or were united in their hatred of Northumbria, it was a mighty army. Penda was portrayed as the aggressor, but we don’t have a Mercian chronicle, which might have told a different story about Northumbrian expansion.

Indeed, the major kingdoms were all expanding at the expense of the smaller ones; Mercia was simply, for a while, more successful at it.

Stained glass window, depicting Penda’s death at the Battle of the Winwaed, Worcester Cathedral. Image credit: Violetriga / CC.

Although Penda was defeated at Winwæd by Oswald’s brother, Oswiu, who subjugated Mercia, a mere three years later Penda’s son, Wulfhere, was able to throw off the Northumbrian yoke and regain Mercian independence. He focused his attention first in the south, driving the West Saxons from their old Gewissan tribal lands in the upper Thames Valley and taking the Isle of Wight and part of modern-day Hampshire.

The kings of Surrey and the South Saxons were his sub-kings and London was also under Wulfhere’s authority; thereafter, the Mercian kings did not lose control of London until the Viking age. Wulfhere’s reign mirrored his father’s, in that by the end of it he was leading a combined force, having ‘stirred up all the southern nations against Northumbria’ but was also unsuccessful in battle.

Wulfhere’s brother, Æthelred, succeeded him. Little of his campaigning activity is recorded, but we know he devastated Kent at least once. At the battle of the Trent in 679 he regained the disputed former kingdom of Lindsey from Northumbria and in 704 seems to have felt that the situation was stable enough for him to retire to a monastery. Cognisant that his son was not up to the task of leading, he left Mercia to his nephew who only reigned for five years. Æthelred’s inept son then ruled briefly but with his death came the end of Penda’s direct line.

Æthelbald and Offa

It was not, however, the end of Mercian ascendancy. The next king, Æthelbald, claimed descent from Penda’s brother and ruled from 716–757. By 731, according to Bede, all the southern kingdoms were subject to him. He witnessed a charter of 736 as rex Britanniae, and in this document he was described as ‘Ruler not only of the Mercians but of all the provinces that go by the general name of “South English”’.

We have no information about how Æthelbald achieved this dominance, although he may have taken advantage of the death and abdication of two other powerful southern kings, Wihtred of Kent and Ine of Wessex. In 740 he devastated Northumbria. An inscription on a commemoration stone known as the pillar of Eliseg, suggests that during Æthelbald’s reign, Powys was also under Mercian domination.

Æthelbald was killed in 757 and, after the now habitual power struggle, the next great king was Offa, the son of Æthelbald’s cousin, who reigned for nearly 40 years. The Northumbrians looked to him for protection, through marriage alliance with Offa’s daughter. The kings of the Hwicce acknowledged him as their overlord, and he conquered the district of East Sussex and reduced the kingdom of the South Saxons to an ealdordom. He lost and then regained control of Kent. He defeated the king of Wessex and when that king died, Offa’s son-in-law, Beorhtric, who may even have been a Mercian, became king of Wessex.

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Offa considered himself the equal of the emperor Charlemagne, though it seems unlikely that view was shared. They quarrelled over trade and marriage alliances, and Offa objected to Charlemagne’s harbouring of Offa’s enemy, Ecgberht of Wessex. Offa saw Ecgberht as a threat, but he cannot have known that his West Saxon rival would found a dynasty whose members would include Alfred the Great.

During a visit to Offa, the king of East Anglia was killed, with later chroniclers blaming Offa’s wife, Cynethryth. Murderess or not, she was certainly powerful, being unique in having coins struck in her name and with her image on them. Offa is also famous for the dyke, and had plenty of resources and manpower to build it. He was described as a tyrant, but as with the kings who preceded him, we only have the enemies’ point of view and much has not survived; Offa’s laws were incorporated into those of Alfred the Great because he found them to be ‘just’, but they are lost to us now.

Offa’s son became king but only briefly and Cenwulf, a distant relative, succeeded. From 798 he controlled the south east; it’s possible he came to some arrangement with Essex, for no more kings were recorded there after his time and he captured the king of Kent, installing his own brother as puppet king there and afterwards taking direct control himself when that brother died. There is less evidence of his influence in Wessex or Northumbria.

The fall of a kingdom

Thereafter, Mercian fortunes tumbled. In a battle of 825 Ecgberht of Wessex ended their ascendancy and Kent, Surrey and Sussex were never again separated from the West Saxon monarchy. Just as a Wessex dynasty was established, Mercia ran out of kings. Since Penda’s line, sons had rarely succeeded fathers and there were always multiple contenders – and often murderous fights – for the throne. It ceased to be a kingdom during Alfred’s reign but retained its influence, not least under the tenure of Alfred’s daughter, Æthelflæd, Lady of the Mercians.

The Kingdom of Mercia (thick line) and the kingdom’s extent during the Mercian Supremacy (green shading). Originally based on a map in Hill, ‘An Atlas of Anglo-Saxon England’. Image credit: Rushton2010 based on Hel-hama / CC.

Annie Whitehead is an author and historian and an elected member of the Royal Historical Society. She has won awards and prizes for her fiction and nonfiction. Mercia: The Rise and Fall of a Kingdom is published by Amberley Books and charts the history of Mercia from its origins up to the last earl in 1071. The paperback edition will be published on 15 October 2020.

Book cover for Mercia: The Rise and Fall of a Kingdom

Annie Whitehead