The triumph of the Anglo-Saxons: how the kingdom of Mercia powered the rise of England

Seen through the prism of those writings, Northumbria and Wessex very much dominate the stories we tell about the Anglo-Saxon world before 900. When we think of the great milestones of early English history, we invariably think of the two kingdoms that occupied the northern third and south-western corner of what’s now England.

• Read more | Alfred the Great and Edington: how the King of Wessex became great

So where does that leave the third great kingdom of the Anglo-Saxon era – Mercia? Without a chronicle to match those produced by Bede and the scribes of Alfred, Mercia’s story can be pieced together only in fragments, like odd strips of film left on the cutting-room floor of history. Largely for this reason, the kingdom that dominated swathes of south-central Britain from the end of Roman rule to the unification of England has been relegated almost to a footnote.

Yet when these strips are assembled, they reveal a truly remarkable story – one every bit as thrilling and consequential as those of Wessex and Northumbria. From obscure origins, in the early seventh century Mercian warlords began to assert their independence from their neighbours, and went on to dominate English politics, culture and trade. By the eighth century, they were making waves in continental Europe; one even styled himself Rex Britanniae: King of Britain. And they lie at the very heart of Anglo-Saxon history.

To fully appreciate why Mercia became such an early medieval powerhouse, you first need an understanding of the landscape from which those ruling warlords emerged. Mercia’s heartland was the modern-day English Midlands, a region that’s geographically blessed. It is framed by three great navigable rivers – the Trent, Severn and Thames – and by many other waterways that run into the Fens.

The two major Roman Roads known as the Fosse Way and Watling Street intersected here, connecting the region with ports and former Roman towns. Extensive fertile plains, tracts of woodland, workable deposits of clay, iron, lead and salt and downland for pasturing sheep were natural assets to be exploited.

• Listen | Anglo-Saxon kingdoms: everything you wanted to know

Medieval powerhouse

Through the earlier Anglo-Saxon period, a number of disparate peoples farmed this land: tribal kingdoms such as the Wreo-ansætan in the north-west; the Hwicce along the Severn and Avon valleys; Middle Anglians in the centre; the Pecsætan of the Peak District; and smaller peripheral communities including the Spaldingas, Gyrwe and Sweodora fringing the great Fens draining into the Wash.

The first warlord to bring these peoples under the banner of the Myrcna rice – the ‘kingdom of the border people’ – was the heathen Penda. He rose from obscurity in the first half of the seventh century, perhaps among the Hwicce, to win victories against first a West Saxon king and then, in alliance with the Welsh, against King Edwin, the Northumbrian who first converted his people to Christianity in 627.

Mercia on the map: The Anglo-Saxon powerhouse spanned a swathe of central Britain

Edwin’s successor, Oswald, recovered Northumbrian fortunes across the best part of a decade, and in 642 brought his army into Mercia to take on Penda. That proved to be a terrible mistake: Penda’s forces destroyed Oswald’s army and dismembered his body, mounting the Northumbrian king’s head and arms on poles at a place that came to be known, in grim irony, as Oswald’s Tree – Oswestry, now in Shropshire.

The following decade, Penda came close to conquering Northumbria itself, but Oswald got his revenge – or at least his family did. In 655, Oswald’s brother, King Oswiu, killed Penda and 30 of his warlord allies in a bloody battle on the river Went in Yorkshire.

Despite this reversal, Penda’s sons and grandsons became Mercian kings. They converted to Christianity, founded churches and forged alliances with their neighbouring Anglo-Saxon kingdoms – Wessex, East Anglia, Kent and Northumbria – while maintaining historical friendships with Welsh kings in the west.

Such alliances were uneasy, and didn’t always hold. In the 670s, a long-running turf war with Northumbria over control of the ancient kingdom of Lindsey, with Lincoln at its heart, was decided definitively in Mercia’s favour after a battle on the Trent.

Trading places

Mercian expansion south to the Thames continued over the next few decades. Initially in the kingdom of Essex, London came under Mercian control around 670. By the beginning of the eighth century, merchants had established trading settlements in four of the Anglo-Saxon kingdoms at places such as York, Ipswich and Southampton. Soon, London itself had become a centre of Mercian royal ambitions, a nerve-centre of trade and a powerful bishopric.

Successive kings granted land and privileges along the Thames to their ministers, bishops and abbots, installing their own officials in the old Roman provincial capital. With Britain’s heartlands open to trade along the Trent, Thames and Nene, and a proliferation of productive monasteries strung out along them, Mercia’s rulers oversaw an economic boom.

Archaeologists have latterly been able to uncover a sophisticated side to life in the Mercian countryside. Excavated settlements show increasing signs of careful planning and of specialisation in areas such as dairy, textiles, leather-working, iron and lead-working. Increasing quantities of silver coins were minted by kings’ moneyers; when they turn up in excavations or through metal-detecting, they are telltale signs of otherwise unsuspected trading sites, often where Roman roads cross important rivers or ancient trails.

Place names, many of which were in the process of forming in the eighth century, offer more clues. Those containing the element burh (a defended royal settlement) surrounded by clusters of ‘functional’ -ton names such as Charlton, Eaton and Burton show how royal administrators were active in planning a network of royal estates controlling strategic locations. Such clusters occur in the Trent Valley – for example, at Tutbury (‘lookout fort’), with Burton and other telltale names close by.

Boosting productivity

Like Bede’s Northumbrian kings, Mercia’s ruling elite encouraged churchmen and women to improve the productivity of their estates. They commissioned Latin scribes to write down their laws and draw up their charters – acting, in a sense, as a civil service. Their now-literate poets began to record their verse, their genealogies and their epic legends in English and Latin.

Mercian rulers also employed the services of sages, healers and prophets. One such, Guthlac – from a noble Mercian family, who lived as a hermit in the malaria-ridden fastnesses of the western fens at Crowland – played a telling role in a turning point in Mercian history.

It was triggered by the death of Penda’s last grandson, King Ceolred, in 716. Penda’s dynasty had dominated Mercia for almost a century, but was now placed in peril by the emergence of a youthful prince – Æthelbald, a cousin of Ceolred, who had exiled him to East Anglia. Having secured the endorsement of Guthlac, Æthelbald returned to Mercia and seized the throne – which he held for an astonishing 41 years.

In Æthelbald’s reign lie the beginnings of a revolution in Anglo-Saxon royal administration. For 20 years, he carefully avoided warfare with his neighbours, investing instead in the soft power of patronage, and promoting wealth through trade. Lundenwic, the trading settlement that grew up on the Thames foreshore at Aldwych, became – in Bede’s words – “an emporium for many nations who come to it by land and sea”.

Æthelbald brought the former kings of the old tribal lands into his council, feasted and honoured them, and presented gifts of imported luxuries in exchange for their loyalty. He granted bishops in London, and his most favoured royal monasteries, exemptions from tolls in his ports – a generous tax break in return for their everlasting prayers and support for his policies.

Increasingly, Æthelbald used the ‘booking’ of rights and privileges by charter to engineer lucrative contracts, and to monumentalise Mercian culture in the landscape. A charter dated to 716–17 records that the king gave the church of Worcester “a certain portion of ground on which salt is made” at Droitwich for the construction of three salt houses and six furnaces, in exchange for six furnaces in two salt houses on the north side of the river.

Such was Æthelbald’s power that in a charter of 736 he styled himself Rex Britanniae: King of Britain – a latter-day emperor. Mercia was now the most powerful English kingdom, and the wealthiest. By the end of his reign, Mercian rule probably extended from the rivers Don and Mersey in the north to the banks of the Thames in the south, and from the Severn to the western fringes of the Wash.

International espionage

The all-conquering king didn’t have everything his own way, though. In 745, Boniface– the English bishop of Mainz on the Rhine – wrote a letter to Æthelbald, asking him to allow a ‘messenger’ – part ambassador, part man of business, part spy – to travel freely throughout Mercia. To make his proposal even more attractive, the bishop also sent a hawk, two falcons, two shields and two lances “as tokens of affection”.

Æthelbald accepted Boniface’s offer, but may have come to regret that decision. Soon Boniface was writing him another letter – this one fizzing with excoriating accusations that the king had been fornicating with nuns rather than taking a lawful wife. This scandalous intelligence had, of course, been gathered by his ‘messenger’.

Nonetheless, Æthelbald bequeathed his almost equally long-reigning successor, Offa, a powerful state apparatus and the bones of a social contract for governance. It was an impressive legacy, and Offa built on it further, forging a fearsome reputation. Even King Alfred’s own chronicler conceded: “There was in Mercia in fairly recent times a certain vigorous king called Offa, who terrified all the neighbouring kings and provinces around him, and who had a great dyke built between Wales and Mercia from sea to sea.”

Offa faced his own challenges, however. He had come to power in 757 after a brief but bloody civil war on Æthelbald’s death. In the following decades he faced rebellion in Kent, frequent Welsh raids, and ongoing conflict with Wessex for control of the upper Thames Valley. Nor were Mercia’s kings immune from the caprices of natural disaster: a great pestilence in 759, and a terrible winter in 763–64 were followed by a summer of drought in which “many cities, monasteries and vills [rural settlements]... were suddenly laid waste by fire”. London was largely destroyed; it was rebuilt, burned again in 798, and rebuilt once more. In 839, it was “an illustrious place”.

Early medieval kings lived their lives on the hoof, travelling with their warbands, counsellors and household between royal estates where they would consume the surplus of the land, dispense judgment and gifts and move on. So Offa must have seen such devastations for himself, but he was above all a man of energy – a builder rather than a destroyer.

His great dyke project fulfilled many functions, including demarcating a zone of control buffering Mercia from Welsh raids, enforcing his rule among formerly independent peoples, and creating a conspicuous monument to himself – long remnants survive to this day.

• Listen | BBC Radio 3's The Essay: Anglo-Saxon Portraits, episode on Offa, King of the Mercians

Other substantial engineering achievements included watermills at Tamworth and Hereford, and a magnificent timber caisson bridge across the Trent at the village of Cromwell in Nottinghamshire. There were very likely trading wharves at London, probably Northampton and at key sites along the Trent near Newark. The age of Æthelbald and Offa saw something very like the first industrial revolution in the English Midlands.

Offa is almost unique among Anglo-Saxon kings in elevating his wife, Cynethryth, to a status that nearly matched his own. She a royal counsellor and witnessed Offa’s char- ters. We cannot say how influential she was in their private conversations, but we know something of her wealth and resolve. She was ceded a prestigious and lucrative religious house at Cookham on the Thames; excavations have shown that it was a successful trading site as well as a convent of nuns.

This early medieval power couple also planned a dynastic legacy. In 787, the new archbishop of Lichfield, Hygeberht, formally consecrated Offa and Cynethryth’s son Ecgfrith as his father’s heir. Then, in about 790, Charlemagne sent an envoy to Mercia with terms under which Offa’s daughter Æthelswith would marry the Frankish king’s son Charles – in diplomatic terms, a condescending favour towards his Anglo-Saxon counterpart. Offa’s impertinent counter-proposal – that Ecgfrith should marry Charlemagne’s daughter Bertha – triggered a diplomatic row and trade embargo lasting several years.

The row was resolved, but no marriage took place. And after Offa died in 796, his son reigned for less than a year before following him to the grave. In any case, a tidal surge of historic change had already crashed against Britain’s shores. Three years earlier, in 793, the Anglo-Saxon Chronicle recorded ominous portents, telling how fiery flashes in the sky were followed by a great famine and then violence when “the harrying of the heathen miserably destroyed God’s church in Lindisfarne by rapine and slaughter”.

Reflecting on this disaster, the Northumbrian scholar Alcuin, asked if this marked the beginning of some greater suffering. It did. The era of Mercian supremacy would not survive the Viking Age.

Power cut

From the turn of the ninth century, Mercian power headed gradually into retreat. This process was accelerated by the rise of a formidable West Saxon dynasty under King Ecgberht, which asserted its own overlordship in the Mercians’ Midlands heartlands. Things got even worse in the 860s when the Viking Great Army invaded Britain and conquered East Anglia. From there they were increasingly able to deprive Mercian kings of control over the east Midlands, eventually leaving them with just a rump territory south of Watling Street and north of the Thames.

The Mercians weren’t finished quite yet, though. Their heyday may have been behind them but they still had a role to play in the evolution of England. When King Alfred conceived a network of defensive burhs to protect his kingdom from Viking attack, he looked to existing Mercian models. When he wanted to revive learning among his people after the defeat of his Viking adversaries, it was to Mercian scholars that he turned – among them Plegmund, who may have helped the king translate important books from Latin into Old English.

In his greatest military victory over the Vikings – at Edington in 878 – Alfred relied on a Mercian king’s army for its decisive support. And the Mercian towns recovered by his children from Viking control – Nottingham, Derby, Lincoln, Stamford, Leicester and others – were the productive bedrock of later Anglo-Saxon England.

• Read more | Alternate history: what if Alfred the Great lost to the Vikings at the battle of Edington?

In short, the legacy of the Mercian realm underpinned the success of Alfred’s children and grandchildren in forging the kingdom of England – which went on to be one of the wealthiest and most powerful states in early medieval Europe. It couldn’t have done it without Mercia.

Marvels of Mercia: 5 must-see sites from the Anglo-Saxon kingdom

Border control: Offa’s Dyke, Anglo-Welsh border

The exact date of construction of this extraordinary feat of royal vision and manpower has still not been established, but no one seriously doubts that it was the work of King Offa. It was studded with strategic look-out points facing into Wales and patrolled by burh-weards – military stewards. Tracing the 177-mile-long Offa’s Dyke Path, now a National Trail, provides a spectacular and rewarding lesson in Mercian history.

House of the holy: All Saints’ Church, Brixworth, Northants

England’s finest surviving Anglo-Saxon church was constructed in the 790s, perhaps by King Offa’s son Ecgfrith. The basilican form, its walls pierced by double-tiered Romanesque arches decorated with terracotta Roman tiles laid on edge, still gives a sense of Mercian ambition, monumentalised in the Midlands landscape. An annual Brixworth lecture celebrates Mercian history and archaeology.

Candy-twist crypt: St Wystan’s Church, Repton, Derbyshire

The early eighth-century minster at Repton was the burial place of kings. The superb mausoleum, surviving as a crypt with narrow arches and candy- twist columns, is perhaps the most atmospheric monument to the great age of Mercia. In the ninth century, a Viking army turned the churchyard into a fortress, with the church as its gatehouse, and buried fallen warriors here.

Salty miracle: Droitwich Spa, Worcestershire

Droitwich may be England’s oldest continually operating industrial settlement. Romans extracted rock and brine famous for its salt concentration – 10 times that of sea water. Mercian kings owned salt furnaces here, and Droitwich salt was traded as a valuable commodity across England and beyond. The town museum, and excavated sites by the canal, reveal a fascinating history.

Royal capital: Tamworth, Staffordshire

The modern street arrangement of central Tamworth still preserves something of the original layout of the fortified Mercian capital, with St Editha’s Church at its heart. King Offa held royal councils here, and a ninth-century watermill has been excavated near the river Anker. The story of Æthelflæd, Lady of the Mercians – who revived Tamworth as a royal capital in 913 – is told among exhibits displayed at the castle.

Timeline: The rise and fall of Mercia

Fifth century AD: 'Anglo-Saxons' arrive in Britain - Angles, Saxons and Jutes from northern Europe - as recorded by Bede (pictured), writing in 731.

c626: The warlord Penda unites tribes of south-central Britain to rule the Myrcna rice (‘kingdom of the border people’) or Mercia. He defeats King Edwin of Northumbria at Hatfield Chase in 633, and kills that ruler’s successor, Oswald, at Maserfield (possibly Oswestry) in 642.

655: King Oswiu of Northumbria avenges his brother Oswald’s death, killing Penda and his allies. Nonetheless, Penda’s sons and grandsons rule Mercia, defeating their north-eastern rivals in 670, and taking control of London.

716: Penda’s grandson King Ceolred dies, and his cousin Æthelbald returns from exile in East Anglia to claim the Mercian throne, endorsed by the influential hermit Guthlac. Ruling for 41 years, Æthelbald launches the transformation of Anglo-Saxon royal administration, industry and trade.

757: After a civil war following Æthelbald’s death, Offa becomes king of Mercia. Over his four-decade rule, he claims the upper Thames Valley from Wessex and repels Welsh raids, building a huge defensive dyke along his western border.

797: Offa’s heir, Ecgfrith, dies after having ruled for less than a year. The resulting period of Mercian decline coincides with the rise of the West Saxons under King Ecgberht and the onset of Viking raids.

865: The Viking Great Army invades England and then, from its initial base in East Anglia, pushes west to take control of most Mercian territory.

878: King Alfred defeats the Vikings at Edington; his greatest military victory relies on a Mercian king’s army.

918: Mercia is annexed by Wessex. Nine years later it is incorporated into the new kingdom of England ruled by Æthelstan, grandson of Alfred the Great.

Max Adams is an archaeologist and author. His new book, The Mercian Chronicles: King Offa and the Birth of the Anglo-Saxon State AD 630–918, is available now, published by Apollo.

This article was first published in the March 2025 issue of BBC History Magazine