LKM: Dumnonia

The kingdom of Dumnonia included Devon, Cornwall and parts of Dorset
The kingdom of Dumnonia included Devon, Cornwall and parts of Dorset

Dumnonia can be a frustrating place to study. There are several concrete records of Dumnonia in the Late Antique-Early Medieval period, and yet when you try to study beyond those few references and archaeological finds you quickly move into legend. It is particularly frustrating considering how long the kingdom of Dumnonia survived against constant Gewisse -Wessex pressure.

A few things seem fairly clear. It is a region where ancient British civilization survived deep into the Medieval period. Even after the English and later Normans took control of the peninsula, actual settlement by outsiders reminded thin. To that end, Oxford University’s population genetics laboratory has begun a project to study the genetics of Cornwall. The development of the Cornish language is also a sign of the antiquity and relative lack of English immigraiton into Cornwall.

During the Roman period, Dumnonia and even more so Cornwall were on the fringe of Roman life. There were no towns west of Exeter and few villas in the fifth century. Exeter was also the civitas capital for the Dumnoni tribe. The sparce Roman infiltration in the penisula is due to a combination of the usefulness of the land and the cooperation of the Dumnoni. The Dumnoni were seamen and miners, both trades were controlled by the Romans, so they had every reason to cooperate with Rome.

In the Late Antique period Dumnonia thrived based on its tin mining and key position on trade routes in the English channel and the Irish Sea. Like some other British kingdoms, Dumnonia initially thrived in the post-Roman period by annexing territory to the east as those regions failed to successfully organize in the post-Roman state. It is likely that Dumnonia once ruled most of Somerset and Dorset as well as Devon and Cornwall. It was a very wealthy area in addition to the tin mining. Somerset and Devon both had well developed Roman estates. Tintagel, one of the most impressive fortresses in Britain, thrived in the fifth century. Historians generally agree that such a great fortress can only have been the home of the king of all Dumnonia. Archaeological remains found at Tintagel confirm that is was the center of a very active Irish Sea trade. Snyder notes, however, that Tintagel’s “exposed position” may indicate it was only seasonly occupied. Yet, this still could support it as a trading hub as traders would have been most common in fair weather. In the fifth century, Irish inscriptions also appear in Dumnonia and Cornwall. Historian Ken Dark has hypothesized that the path these inscriptions cut across the peninsula indicates a route toward the continent from Tintagel to ports along the English Channel. This same route is also recorded in the Life of St. Samson of Dol, written in the sixth century, one of the earliest witnesses to Late Antique Britain. Dumnonia and Cornwall were a majority of the land route between Wales and Brittany in the fifth and sixth century. Involvement in the migration of so many saints from Wales to Brittany, Dumnonia/Cornwall has a very high visibility in the veneration of British saints and up to 140 are memorialized in Cornish churches and chapels.

The Anglo-Saxon Chronicle records the first really major Anglo-Saxon victory against the south west in 577 when the Gewisse slew three kings — Conomael, Condida, and Farinmael– and took the cities of Gloucester, Bath, and Cirencester effectively cutting Dumnonia off from the rest of Britain by land. Before this event, the Gewisse appear to have been confined to the upper reaches of the River Thames, east of Gloucester.  Dumnonia almost certainly took advantage of their neighbors defeats and moved into at least part of Dorset.  It is unclear exactly how damaging this was to Dumnonia though because they were masters of the sea and would have had fleets in the English channel, the Irish Sea and the Bristol Channel (Severn estuary). They were known to maintain active contact with Brittany where a post-Roman British kingdom of Dumnonia was also founded by British immigrants.

Constantine Corneu

Constantine Corneu is considered the dynastic founder of the kingdom of Dumnonia-Cornwall. He is usually linked with the Constantine rebuked by Gildas in his manifesto On the Ruin of Britain [ch. 28]. This vile Constantine is said to be the “son of the unclean lioness of Damnonia”. How a Constantine of Dumnonia gained the epithet Corneu, indicating Cornwall is unclear. His epithet may suggest that either the royal family emerged out of Cornwall or that this Constantine was capable of bringing Cornwall securely under the control of Dumnonia. Cornwall as probably kept as a subkingdom of Dumnonia. Gildas is believed to have written his manifesto in the 540s.

Gildas claims that Constantine, dressed as a monk or abbot, murdered two royal youths in church and splattering blood over the sanctuary within a year of taking a sacred oath. He goes on to claim that Constantine had put away his wife and committed frequent adultery.  It sounds as though Gildas is describing some fairly common late antique methods of securing the throne – eliminating rivals who were seeking sanctuary in a church and making a more advantageous marriage. Gildas’ manifesto has been dated to about 540, so we can identify Constantine in the Dumnonian royal pedigree as the father of Cado.

Gildas made this wicked king immortal by writing about him. Constantine and the murder in church has become a consistent theme in British legend. Geoffrey of Monmouth puts this story to use when he had Constantine murder Mordred’s sons in church after Arthur’s death.  Constantine or his son Cado become Arthur’s successor (and then the throne passes to the other four of Gildas’ kings).

For all of Gildas’ rebukes and his later Arthurian reputation, it has been suggested that he is the St Constantine briefly eluded to in some British sources. If so, this would suggest that the first three generations of the Dumnonian were considered saints : St Constantine, St Erbin, and St Gerren (Geraint). Little is known of Constantine’s son Erbin who was considered a saint and is mentioned in Bonedd y Sant.

Geraint of the Fleets

Erbin’s son Geraint (Gerren) is the most famous Dumnonian king. He is known as Geraint of the Fleets and in the Welsh Triads was one of the three great fleet owners of Britain. His name testifies to Dumnonia’s reputation as a naval power. In his time the great fortress of Tintagel was probably active and trading with the continent was still in full swing. He is the Geraint absorbed into Arthurian lore and mentioned in Y Gododdin as Geraint from the South. He is the inspiration for the tale of Geraint and Enid which either is derived from or inspired Erec and Enid. Given that Geraint’s Dumnonia was in close contact with Brittany, his reputation would have easily passed to Breton bards and on to the French. Preservation of tales of Geraint and Dumnonia would have only been aided by Dumonia’s role in the immigration route to Brittany and continuing ties across the channel. Geraint is perhaps best memorialized in the Old Welsh poem, the Battle of Llongborth, written in two of the four ancient books of Wales.

Before Geraint, the enemy of tyranny,
I saw horses white with foam,
And after the shout, a terrible torrent.

In Llongborth I saw the rage of slaughter,
And biers beyond all number,
And red-stained men from the assault of Geraint.

In Llongborth I saw the edges of blades in contact,
Men in terror and blood on the pate,
Before Geraint, the great son of his father.

In Llongborth I saw the spurs
Of men who would not flinch from the dread of the spears,
And the drinking of wine out of the bright glass.

In Llongborth I saw the weapons
Of men, and blood fast dropping,
And after the shout, a fearful return.

In Llongborth I saw Arthur,
And brave men who hewed down with steel,
Emperor, and conductor of the toil.

In Llongborth Geraint was slain,
A brave man from the region of Dyvnaint,
And before they were overpowered, they committed slaughter.

Exerpt from the Battle of Llongborth,

Red Book of Hergerst & Black Book of Carmarthen

This poem is usually believed to refer to Geraint ap Erbin, but this may be unduly influenced by the reference to Arthur. If the Arthurian reference is not used to date it, then it could be either Geraint ap Erbin or his late seventh century namesake.

Geraint ap Erbin is given at least two sons in Welsh pedigrees — Cado ancestor of King Judhael and Selyf father of St Cybi (Kyby) of Holyhead in Gwynedd.


Geraint ap Erbin is said to have been succeeded by his son Cado / Cadwy. Little is known about him except for his place in some genealogies and Arthurian lore.

King Geraint and Bishop Aldhelm

Today the best known Dumnonian king is King Geraint (fl. 700) who corresponded with St Aldhelm over British church practices, namely the calculation of Easter and the British tonsure. The letter was written shortly after the the council of Hertford in 672.  Geraint was one of the primary military opponents of King Ine of Wessex. The Saxon monastery phase at Glastonbury Tor did not begin until the time of King Ine. Snyder notes that two early abbots of Glastonbury were named Welahstod adnd Cealdhun/Wealdhun (both including the Welsh -wealh), and cults of British saints including Patrick, Gildas and others along with King Arthur were remembered fondly at Glastonbury. William of Malmesbury records all of these British legends as being quite active in his time. Further a king Gerontius (Gerraint) granted land to Sherborne abbey in Dorset and beside the river Tamar at Maker (Macuir). This long reigning King Geraint is recorded fighting King Ine and Nunna in 710. If the King Geraint who falls at the battle of Longborth is this Geraint is may signal the loss of Devon to Wessex. If  a single King Geraint ruled from c. 672 to at least 710 it is likely that is entire eastern flank was a constant military zone with the kings of Wessex, and King Ine for most of that time.  Geraint’s sucessors were able to hold the line against Wessex and British victories are recorded in the Annales Cambriae at Hehil (722) and conflicts are not recorded again until Egbert of Wessex needed military adventures in 814. Cornwall’s independence seems to have eneded within the next generation.

Æthelstan and Dumnonian Control

Yet, even after the English took dominion over Dumnonia they seem unable to tame it. The annals are silent on Æthelstan’s activities in Cornwall and Devon but William of Malmesbury provides crutial information:

Æthelstan “attacked them [the Britons of Dumnonia] with great energy, compelling them to withdraw from Exeter, which until then they had inhabited on a footing of legal equality with the English. He then fixed the left bank of the Tamar as the shire boundary, just as he made the Wye the boundary for the North Britons. Having cleansed the city of its defilement by wiping out the filthy race, he fortified it with towers and surrounded it with a wall of square-hewn stone.” (William of Malmesbury in Snyder, 2003, p. 169).

What is really remarkable here is that it was as late as Æthelstan before Devon and Cornwall came under strong English rule. Snyder notes that contacts between Æthelstan and Brittany, including the importation of Breton relics began around this time. This all suggests that the expansion of Wessex westward was relatively slow.

Tristan and Isolde, German woodcut from 1484
Tristan and Isolde, German woodcut from 1484

Tristan and Mark

The story of Tristain, Isolde and Mark has always focused on Cornwall. There is some scant evidence that it is a story of Dumnonia. There is a highway memorial stone to Drustan son of Cunonmor (Cynfawr, Hound of the Sea) in Cornwall. Wrmonoc’s Life of St Pol de Leon refers to a King March, also known as Conomor.It has long been thought that some kings may have ruled on both sides of the English channel, allowing the Breton Mark, aka Conomor, to have also ruled in Cornwall. Snyder summerizes these refernces this way:

“This string of evidence has led many to conclude that Cynfawr/Cunomorus was the sixth century lord of Castle Dore and the King Mark of Tristan legends (and Arthur’s nemesis March in the Welsh Triads). Complicating matters, however, are two earlier continental refernces to Cunomorus: Gregory of Tours describes him as a Breton count, and in the Life of St. Samson he is a minor Breton lord of Carhaix who rebels aginst Judheal, king of Dumnonee. Either Cunomorus held authority in Britain and Brittany, or genealogies are confusing two different rulers.” (Snyder, 2003, p. 166-167)

It should also be noted that the other area of Britain sometimes associated with the story in Galloway and the area of the Clyde where the Mote of Mark and Trusty’s Hill are located was also recorded in the Roman period to belong to a tribe called the Damnoni. The extreme similarity of the names Dumnoni and Damnoni may suggest that this was once a single tribe. As they would have both been closely associated with trade it is not impossible that ties continued between these two tribes. Indeed the two tribes could have had a very profitable trade going with the northern Damnoni (of Strathclyde) sending slaves south and northern goods for trade and the southern Dumnoni sending goods from the continent northward. (St Patrick refers to fifth century slave raiding by Strathclyde in Ireland in his letter to Coroticus.)


Ken Dark (1994) Civitas to Kingdom: British Political Continuity 300-800. Leicester University Press.

Christopher Snyder (2003) The Britons (The Peoples of Europe)Blackwell.

2 thoughts on “LKM: Dumnonia

  1. Hello,

    What are the arguments for Dumnonia to have extended as far eastwards as Somerset? I know it’s a pretty popular view, but on archeological grounds (as recently studied by Stuart Laycock for a survivance of pre-roman tribal identities in post-roman Britain) the civitas of the Durotriges appear to have been pretty distinct from Dumnonia. Ken Dark also proposed that Gildas wrote in Durotrigia, this could explain why no ruler from this area is known from sources.

    The existence of a continental Dumnonia in Brittany have recently been examinated by Magali Coumert whom concluded it was a later make-up from the scriptorium of Landévennec abbey. For her it’s quite possible that the Dumnonia referenced in the 7th or 8th century Vita Prima Samsonis is the insular one.

    Best Regards,

    Benjamin Franckaert (from Brest, Brittany)

Comments are closed.

Create a free website or blog at

Up ↑

%d bloggers like this: