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Celtic Kingdoms of the British Isles

Celts of Cymru


Deheubarth (Wales)

FeatureThe expulsion of Roman officials in AD 409 (see feature link), meant that Post-Roman Britain struggled on without support from continental Europe. It faced plague, mercenary revolt, civil war, and a general break-down in trade, communications, and unity. Over the course of about three centuries the Britons gradually lost the entire west and centre of the island to Germanic invaders.

In the west, largely in what would become modern Wales, the end of national unity seems to have started earlier and taken place more quickly. Even by the start of the fifth century it is apparent that several territories had emerged here, with later tradition claiming the creation of the 'kingdoms' of 'North Wales', 'South Wales', and 'Mid-South Wales'. North Wales became Gwynedd, while South Wales became Dyfed, and these two states, along with Powys, formed the largest principalities in the surviving western British territories. They never in reality used the English term, 'kingdom'.

The 'kingdom' of Deheubarth (pronounced de-hay-bath) was formed as a unified state which comprised much of the territory of the preceding - and smaller - territories of Dyfed, Ystrad Tywy, and Seisyllwg. Virtually all of Cymru (Wales) was unified under Rhodri Mawr in the mid-ninth century, although individual principalities retained their own rulers who accepted Rhodri's overlordship. Those states survived for some time afterwards, and it was only during the reign of Hywel Dda that they were formally merged into a new, expanded state known as Deheubarth, thanks to some fruitful marriage alliances.

Hywel Dda was the son of Cadell of Seisyllwg. In 904 he and his father conquered Dyfed, and then in 942 he conquered Gwynedd. By then, and from his accession in 916, he was already able to claim to rule a greater South Wales. Now he controlled all of Wales, a personal union which survived until his death. Then Gwynedd detached itself from the remainder of the territory, making Dyfed the heartland of Deheubarth along with the territory of Seisyllwg (ancient Ceredigion).

Despite it proving impossible to maintain a fully unified Wales after his death, it was Hywel's descendants who ruled large areas of the country, often with traditional borders changed by the shake-up. As a general rule, the princes of Gwynedd remained militarily dominant, while Deheubarth was either ruled by vassals or directly by Gwynedd's ruler.

The word 'deheu' means 'of the south', the state's obvious power base in relation to the rest of Wales. The suffix 'barth' means 'part' in the sense of a region, from 'parthau', so 'of the south part [of Wales]'. Its territory included the modern county of Dyfed (old Carmarthanshire, Pembrokeshire and Cardiganshire), and Brycheiniog (now in southern Powys). It also occasionally included the principality of Gwynedd, but usually only when Gwynedd's prince (from the Latin 'princeps') was also prince of Deheubarth.

Rhuddlan Castle in Wales

(Information by Peter Kessler, with additional information by Hywel George and Edward Dawson, from A History of Wales from the Earliest Times to the Edwardian Conquest, Volume 1, Sir John Edward Lloyd (Longmans, 1912), from Welsh Genealogies AD 300-1400, Peter Bartrum, from The Oxford History of England: Anglo-Saxon England, Sir Frank Stenton, from Welsh Medieval Law, Arthur Wade-Evans, 1909, from Æthelstan: The First King of England, Sarah Foot (2011), from Kings and Kingdoms of Early Anglo-Saxon England, Barbara Yorke, and from External Links: Encyclopaedia.com, and Ancient Wales Studies.)

844 - 873

Rhodri Mawr 'the Great'

Ruler of Wales (Gwynedd, Dyfed, & Seisyllwg).


FeatureThe Chronicle of the Princes reports that 'Saxons' (probably from Mercia) invade Anglesey. Meurig ap Hywel of Gwent is said to join Rhodri 'the Great', ruler of Wales (Gwynedd and Deheubarth), in defeating them but falls during the battle. The Annales Cambriae (see feature link) also record the death of Meurig at the hands of Saxons (meaning the English).

Rhodri Mawr
There never was a king of Wales (a Germanic title, while the Welsh used the Latin princeps) but Rhodri Mawr perhaps came closest to achieving the reality of either, uniting all of the Welsh principalities under his control but then undoing the process by ensuring that they were divided amongst his sons upon his death

872 - 873

The death of Gwgan ap Meurig of Seisyllwg means that his principality passes to his brother-in-law, Rhodri Mawr. Rhodri is now ruler of all Wales, and in 873 he institutes a form of devolved government in which three of his sons control parts of the country in his name. Anarawd is granted Deheubarth, Cadell governs Seisyllwg, and Merfyn commands in Powys.

873 - 916

Anarawd ap Rhodri

Ruler of the south (and Gwynedd in 878).


Upon the death of Rhodri Mawr, and according to his wishes, Wales is officially divided between his sons. Anarawd succeeds him in Deheubarth and gains Gwynedd, Merfyn is confirmed in Powys, and Cadell in Seisyllwg.


MapHywel Dda is the son of Cadell of Seisyllwg and also ruler of Dyfed (and therefore the nephew of Anarawd). He rules the latter from 904, and in 916 becomes ruler of Deheubarth, creating a permanent greater South Wales state (see map link).

When he becomes ruler of Gwynedd in 942 he is able to create a united Wales. Gwynedd becomes detached from the remainder of the territory in 950, but this allows former Dyfed to provide the heartland along with Ceredigion of the state of Deheubarth.

916 - 950

Hywel Dda 'the Good' ap Cadell

Ruler of Wales (Dyfed (904), Gwynedd (942) & Seisyllwg).


After being crushed by Mercia, the increasing supremacy of Deheubarth in southern Wales forces Brycheiniog to submit some of its power and it effectively becomes a sub-kingdom. Tewdr Brycheiniog still exercises regional power though, being witness to an English charter of 934.

Map of England and Wales AD 900-950
By the dawn of the tenth century the period of invasion and conquest by the Vikings, mostly originating from Denmark or Viking Dublin, had ended (click or tap on map to view full sized)


Æthelstan of Wessex and all the English meets with several northern kings at the convention of Eamont (near Penrith) and later meets with the Welsh princes, including those of Deheubarth, Glywyssing, and Gwent. All accept him as their overlord. Once he assumes overlordship of British Corniu, and ousts the Danish king of York, all in the same year, he is well and truly king of all the English.


Hywel Dda gains Gwynedd upon the death of Idwal Foel and grabs Powys, making him sole ruler of all Wales. He has already acknowledged the late Athelstan of Wessex as his overlord and has associated himself closely with the English king, witnessing Athelstan's grants of lands and charters.

The British Museum possesses a charter which records a grant of land by Athelstan at Luton in 931, and which bears the testimony: 'Ego Howael subregulus consensi et subscripsi' ('Sub-King Hywel hereby consents and agrees').

It is clear that Wales is now sharply divided between a strong anti-English party, based chiefly in the north and led by the sons of Rhodri Mawr in Gwynedd, and a South Welsh party which favours union with England. Hywel is the leader of the latter, and his epithet 'dda' ('good') is given to no other Welsh ruler.

Hywel Dda of Deheubarth and Wales
Unusually for the dominant rulers in later medieval Wales, Hywel Dda was a man of the south, having been the driving force behind the creation of Deheubarth out of several smaller states and territories (this 1909 oil imagines the prince's appearance)

It is probably first given to him by the South Wales 'unionists'. The older epithet of 'mawr' ('great') which had been applied to Rhodri Mawr had probably arisen as an expression of the traditionally more exclusive nationalist policy of the North Welsh. These conflicting views dominate Welsh politics for the next couple of centuries and still retain echoes into the modern day.


Cadwgan, son of Owain and grandson of Hywel Dda, is killed by the 'Saxons' of England. In the same year a battle takes place at Carno between the sons of Idwal Foel of Gwynedd and the sons of Owain ap Hywel Dda. The men of Gwynedd manage to devastate areas of Dyfed, presaging a great deal of future conflict between the two greatest states of Wales.


The death of Hywel Dda, ruler of all Wales, leaves the country divided. Hywel's sons, Owain, Rhun, Rhodri, and Edwyn, take possession of his estates in South Wales, with Rhodi becoming ruler of Deheubarth itself and Owain becoming prince of Ceredigion (Seisyllwg). Iago and Ieuaf, the sons of Idwal Foel, seize North Wales as their birthright (Gwynedd and Powys).

The two sides disagree strongly over the break-up of a united Wales, but the joint rulers of Gwynedd cannot be removed, despite a raid into Dyfed which sees many of their men cut down by Owain's force from Ceredigion. Morgannwg continues to retain its independence under its own line of rulers.

Castell Nos in Glamorgan
Castel Nos, a medieval fortress, was built above the forest to the east of Maerdy in Glywyssing by the Welsh lords of Meisgyn, descendants of the last king of Morgannwg

950 - 957

Rhodri ap Hywel

Son. Ruled all Wales but could not retain Gwynedd.

950 - 954

Edwyn / Edwin ap Hywel

Brother. Co-ruler. Predeceased Rhodri.

952 - 953

As part of the ongoing conflict between Deheubarth and Gwynedd, Owain, prince of Ceredigion (Seisyllwg), leads an army into the northern Welsh principality and engages its men at the Battle of Aberconwy. The fighting is so fierce that both sides are forced to withdraw, having sustained heavy losses. The following year, Gwynedd repays the compliment, invading and devastating Ceredigion and being driven out by more fierce fighting.


Rhodri's surviving brother, Owain (not to be confused with the earlier Owain ap Hywel of Glywyssing (886 - circa 930)), succeeds to the throne of Deheubarth. That territory and Ceredigion (Seisyllwg) are fully reunited under him as its single ruler seeing as Edwyn has already died.

957 - 986

Owain ap Hywel

Brother. Ruled all Wales but Gwynedd.


Owain swears to pay an annual tribute to King Edgar 'the Peaceful' of England. Edgar is just eleven years away from being ritually anointed as the head of the 'Anglo-Saxon Empire' at Bath. His reign sees a major change as English local government is reorganised on the basis of shires.

FeatureThe English Church is also reorganised and coinage is reformed, while it is Owain who is instrumental in the formation of a version of the Annales Cambriae ('Text A' - see feature link).

986 - 999

Maredudd ap Hywel

Brother. Ruled all Wales including Gwynedd.


Following the death of Owain ap Hywel of Deheubarth it is his son, Maredudd ap Owain, who rules both Deheubarth and Gwynedd, having conquered the latter during his father's reign (towards its very end). The two principalities are reunited for several generations, usually along with Powys.

The mountains of North Wales provided a powerful refuge for the rulers of Gwynedd in times of trouble and a wonderfully scenic backdrop to their resistance to Norman and Plantagenet rule

999 - 1005

Cynan ap Hywel

Brother. Ruled all Wales including Gwynedd.

1005 - 1018

Edwin ap Einion

Grandson of Owain.

1005 - 1018

Cadell ap Einion

Brother. Co-ruler.

1018 - 1023

Llywelyn ap Seisyll

Maredudd's son-in-law. Ruled all Wales including Gwynedd.


Llywelyn ap Seisyll of Gwynedd and all Wales dies unexpectedly and Rhydderch ap lestyn seizes the throne of Deheubarth by force, albeit holding onto it briefly. However, the interruption allows Gwynedd's native princes to regain ascendancy over those of Deheubarth.


Rhydderch ap lestyn

Ruler of Morgannwg. Usurper.

1023 - 1033

Iago ap Idwal of Gwynedd swiftly pushes out Rhydderch and re-establishes the domination of his northern principality over south-western Wales. Deheubarth's hold on the north has been broken.

1023 - 1033

Iago ap Idwal ap Meurig ap Idwal Foel

Brother. Ruled all Wales including Gwynedd.

1033 - 1045

Hywel ab Edwin

Son of Edwin ap Einion.

1033 - 1035

Maredudd ab Edwin

Brother and co-ruler. Died.


Upon the death of the last ruler of Brycheiniog, the principality is divided between his sons, and all effective power passes to Deheubarth. More concretely fixed to 1045 is the fact that Gruffydd ap Rhydderch of Morgannwg is able to seize Deheubarth from the overlordship of Gruffydd ap Llywelyn of Gwynedd and hold onto it for a decade until the tables are turned.

Brecon Beacons
The fluctuating fortunes of the state of Brycheiniog took place in the dramatic landscape of the Brecon Beacons in south-eastern Wales, on Deheubarth's eastern border

1045 - 1055

Gruffydd ap Rhydderch

Ruler of Morgannwg. Killed in battle.


Gruffydd ap Llywelyn of Gwynedd invades and conquers Morgannwg and Gwent, subjugating them both and drawing them directly under his control along with Deheubarth as part of a united Wales.

1055 - 1063

Gruffydd ap Llywelyn

Ruler of Gwynedd, Deheubarth, Gwent, Morgannwg, & Powys.


After uniting all of Wales and becoming the first recognised prince of Wales, Gruffydd is killed by disaffected Welshmen. His head is sent to Harold Godwinson and King Edward the Confessor of England as the price of peace following attacks on England by Gruffydd.

With Gruffydd's half-brother Blethyn of Deheubarth gaining Gwynedd in his place (closely allied to his brother, Rhiwallon who may share control), he rules a still-mostly united Wales. Powys is detached for, or by, his son. This division may happen in 1063 as an informal devolvement of power by Blethyn himself to avoid later dynastic squabbles, but it is certainly confirmed upon his death in 1075.

1064 - 1072

Maredudd ab Owain ab Edwin

Grandson of Edwin ap Einion. Rule uncertain. Killed in battle.

1066 - 1068

The last native British earl of Corniu (Cornwall) is deposed by William of Normandy in 1066 as he tightens his grip on the newly-conquered kingdom of England. At first, only the south-east can be considered as being securely held.

Danish axe head
There was heavy fighting around London Bridge between Danes and English during the early 1000s, and this axe head was found with many others at the bridge's north end, possibly lost in battle or thrown into the Thames in celebration (courtesy Museum of London)

Princes Blethyn and Rhiwallon ap Cynfyn of Gwynedd, Deheubarth, and Powys resist the invaders as part of their supporting role for Harold Godwinson. They join Eadric 'the Wild' of Mercia in an attack on Norman forces at Hereford in 1067, and those of Earl Edwin of Mercia with Earl Morcar of Northumbria in a further attack in 1068.

1072 - 1078

Rhys ab Owain

Brother. Killed by Morgannwg.


With the death of Rhys ab Owain at the hands of Caradog ap Gruffydd of Morgannwg, the principality is seized by Rhys ap Tewdwr Mawr, a second cousin by way of a younger son of Einion ap Owain ap Hywel. Gruffydd ab Maredudd, nephew of Rhys ab Owain and the son of his brother, Maredudd, is never able to claim his birthright.

1078 - 1093

Rhys ap Tewdwr Mawr

Cousin. Ruled all Wales but Gwynedd. Driven out briefly.


Attempting to emulate the achievements of his father and grandfather and become ruler of South Wales, Caradoc ap Gruffydd of Morgannwg drives Rhys ap Tewdwr Mawr from his throne. He is immediately faced by the threat of that ruler returning in alliance with Gruffydd ap Cynan, who is pursuing his own claim for the throne of Gwynedd.

Gruffydd also gains the cooperation of his nemesis in Gwynedd, Trahaern ap Caradog, and Meilir ap Rhiwallon of Powys. Caradoc is killed at the Battle of Mynydd Carn, as are Trahaern and Meilir, allowing Gruffydd to seize his birthright in Gwynedd and Rhys to regain Deheubarth.

The Norman conquest of Britain owed much to good fortune, but once achieved it was enforced by military strength and a prolific castle-building programme

1093 - 1113

Rhys ap Tewdwr Mawr has been successful in fighting off several attempts to dethrone him, but now he dies in mysterious circumstances while resisting the expansion of Norman power in neighbouring Brycheiniog. It may be Bernard de Neufmarché, the Norman lord who has taken control of Brycheiniog, who slays him.

His son, Gruffydd ap Rhys, is forced to flee, becoming a fugitive for a time before he can escape to Ireland. Deheubarth has apparently been conquered, and is carved up between rival Norman lords, each taking their share of the existing cantrefi or lordships.

1113 - 1114

Gruffydd ap Rhys returns from Ireland intent on reclaiming the throne of South Wales which is in the hands of the Norman king. Henry II sends orders to have him arrested but he finds refuge with Gruffydd ap Cynan in Gwynedd.

Received at the palace of Aberffraw with full honours, he is soon joined by his brother, Hywel ap Rhys, who has escaped from years of imprisonment at Montgomery Castle under the watchful eye of Arnulp de Montgomery.

Henry destroys the impending Welsh alliance by offering Gruffydd ap Cynan gifts of tribute-free lands, and the brothers are forced to flee to Ceredigion and the wilds of Ystrad Tywy. From there they begin to attack Norman strongholds in Ceredigion and North Pembroke (the heartland of former Dyfed).

Llanstephen Castle in Wales
The rough stone walls of Llanstephen Castle in the modern county of Carmarthenshire were put up by the Normans in order to solidify their gradual conquest of South Wales, but they didn't always command the castle - in 1146 it fell to Deheubarth

Several castles are destroyed or severely damaged while England suffers from a plague and is unable to respond. Flemish mercenaries are offered lands in Wales, particularly in Pembroke, in return for stemming the advance, and Gruffydd is only able to restore a reduced Deheubarth, with the rest still being held by Norman lords.

1113 - 1137

Gruffydd ap Rhys

Son. Ruled a reduced Deheubarth.

1137 - 1143

Anarawd ap Gruffydd

Son. Ruled all but Gwynedd. Murdered.

1143 - c.1151

Cadell ap Gruffydd

Brother. Severely injured by Normans. Died 1175.


With Anarawd having been murdered on the orders of a Norman lord, Cadell succeeds him and takes the fight to the Normans. He captures castles at Llanstephen and Carmarthen, the latter of which he is able to hold for the remainder of his reign, refortifying it in the meantime.

c.1151 - 1155

Maredudd ap Gruffydd

Brother. Died.

1155 - 1197

Rhys ap Gruffydd

Brother. 'The Lord Rhys'.

1163 - 1165

Deheubarth is invaded by Henry II Plantagenet. Rhys is captured and imprisoned for a few weeks before being allowed back to command a small portion of his former lands. Now in alliance with Owain Gwynedd, he is able to retake most of his former territory in 1165 when one of Henry's attacks on Wales is defeated.

Henry II Plantagenet
Henry II of England and Normandy, son of Empress Matilda and Geoffrey of Anjou, died having added half of France to his possessions, making him one of the most powerful rulers in Western Europe


Following the death by natural causes of the Lord Rhys, what is left of his principality in the face of increasing pressure by the Plantagenet kings is divided between his feuding sons. They seem more interested in fighting one another than in preventing Plantagenet advances. Even when Gruffydd dies, Maelgwyn is unable to end the feud, seizing more land which he rules until his own death.

1196 - 1202

Gruffydd ap Rhys

Son. Ruled from May 1196. Died of illness.

1196 - 1230

Maelgwyn ap Rhys

Brother. Ruled certain areas of the principality.

1202 - 1236

Owain ap Gruffydd

Son of Gruffydd. Last South Wales independent native ruler.


The power of Deheubarth has been declining for years, and by this point the practical end of the ruling dynasty has arrived. Deheubarth is subjugated under Plantagenet rule. The sons and grandson of Rhys 'the Hoarse' continue to govern in three pockets of territory until 1283 when any pretence towards Welsh independence is ended by Edward I.

First Barons War illusration from the Battle of Lincoln 1217
The First Barons' War in England saw a collection of the powerful baronial class rise up against King John, determined to force him to abide by Magna Carta but weakening their own cause by accepting support from France

In 1284 the Statute of Rhuddlan divides the Dyfed region of Deheubarth into the counties of Carmarthenshire (which contains only a small, eastern part) and Pembrokeshire (which contains much of Dyfed). Both counties survive in use today. One of the principality's royal sons, Owain Glyndwr, 'Prince of Wales', later leads a rebellion against Wales' overlords which ends in 1416.

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