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Post-Roman Britain


by Peter Kessler, 25 November 2012. Updated 8 December 2018

Between AD 468-469, a man described as the king of the Britons crossed the English Channel to Gaul, bringing 12,000 ship-borne troops with him.

This 'king', Riothamus, remained in Gaul for a year or more, advancing to Bourges in central Gaul, and even beyond. He teamed up with other parties who were interested in maintaining imperial order in Gaul against the growing threat presented by the Visigoths in Hispania and southern Gaul. However, Gaul's imperial prefect, the deputy of the Western Roman emperor, treacherously undermined him by dealing with the Visigoths.

A battle ensued near Bourges in 469 between the Britons (possibly bolstered by units of Armorican Bretons), and an overwhelming force of Visigoths. The Britons were eventually defeated when no imperial forces came to their assistance, thanks to the treachery of the prefect. Riothamus escaped with the remnants of his army into the nearby territory of the Burgundians, never to be heard of again.

The imperial forces, which consisted of a combined army of Romans, troops from Soissons under Comes Paulus, and Burgundian foederati, were subsequently defeated in a second major battle. Paulus was probably killed, and Soissons and Armorica were now cut off from Rome, never to be regained.

Riothamus the Briton or Breton?

The identity of Riothamus has always been a mystery.

The events of 468-469 were recorded reliably enough, but with the 'king's' identity somewhat obscure. Until recently most historians have labelled him a Breton, one of the British migrants in Armorica (modern Brittany), and have dismissed the event as a relatively unimportant Breton attempt to be a player in Gaulish politics of the fifth century.

The available evidence, though, does not specifically state that he was a Breton [1].

True, there is a 'Riotham' in the lives of some of the Breton saints. He is claimed as the son of King Deroc of Dumnonee, although the 'Lives' state this is Deroc II while other evidence says that he is the grandson of Guitol (father of Deroc I). According to that evidence, he is exiled to Britain following the death of his father, but he eventually returns and kills the usurping general who has taken his inheritance. This either makes him a contemporary of or the same man as Riothamus, or someone from a couple of generations later in time who had been named in his honour.

Those who relegate Riothamus to being a more minor Armorican prince tend to ignore the fact that he travelled by sea to reach Gaul, which he certainly wouldn't have had to do to get there from Armorica. It seems much more likely that he was a British leader (whatever his origins), one who, perhaps, had largely pegged back the Saxon and Jutish threat in Britain itself by this time [2].

His expedition is very much in the tradition of Magnus Maximus, Constantine III, and even various Roman usurpers of previous centuries in Britain. All of them withdrew troops from Britain to fight in Gaul. All of them were ultimately defeated, although in the case of Riothamus, it is not certain that it was due to the treachery of the prefect of Gaul. This official, one Arvandus, had sent a message to the Visigoths stating that the Britons beyond the Loire should be attacked, meaning either Riothamus and his army, or the Armorican Britons in general. The chronology is open to interpretation, and Arvandus could have been arrested and shipped to Rome before the arrival of Riothamus. But either way, the threat to British interests was a very real one.

With slight spelling variations (Riotimus, Riutimus, Riatham), this mysterious British leader is referred to by Continental writers as not only the king of the Britons (Jordanes) but as Riothamus. Something which has only been realised more recently is that this is not a name. It Latinises a title or honorific in the British language, Rigotamos, in much the same way as as 'Vortigern' is a title rather than a name. This particular title meant something along the lines of 'supreme king' or 'supremely royal'. This is far from unique in history, with a much more famous example being Genghis Khan, which means 'Very Mighty Ruler'.

Edward Dawson points out that while 'Rio' as a shortened form of 'Rigo' ('king') is exactly right, the next element appears to be an unrecorded cognate of the Latin 'dominus' or 'domno', which means 'master' or 'lord'. In this case it would mean the high king, or the lord of kings. The element also occurs in a royal name among the Catuvellani tribe of pre-Roman Britain. Togodumnus was literally Lord Dagda, a deity-based name.

A later look at the same name produces an alternative theory, though. Very early the Britons dropped the 'x' sound from words, so that Saxon became Saison, for instance. In this manner, the Celtic 'rigo' or 'rix', would become 'rio'. The remainder of the title, 'thamus' without the Latin '-us' nominative suffix is 'tham'. In the process of undergoing change from Brythonic to early Welsh, many times a 'd' or 't' would end up as a 'dd' (voiced as a 'th'); but this particular change could be before the Brythonic 'm' altered to a 'v' (spelled 'f' in Welsh). This leaves either 'tam' or 'dam'.

[1] There may not even have been any serious differentiation between insular and Continental Britons at this time, as Armorica seems largely to have been treated as an extension of the territory of the kingdom of Dumnonia in south-western Britain.

[2] There is a notable drop-off in barbarian activity in Britain by the late 470s and during the 480s, as would-be adventurers saw better promise of glory and riches in Gaul in preference to facing the now-veteran defenders of Britain.

The latter shows promise. The name Riothamus can be broken down into 'King of Dam', meaning Damnonia or Dumnonia. People may simply have shorted Dumnonia into Dam, and it would either be the Dumnonia of south-western Britain or the Domnonia of Armorica rather than the northern British Damnonii. This helps to support the idea of him being the son of Deroc of Domnonia. He could both be Deroc II and Riothamus, official name and honorific nickname respectively.

The use of 'Riothamus' suggests that this leader was at least nominally another high king like Vortigern, and perhaps his successor. That would probably put him in the same peer group as Ambrosius Aurelianus, another historically-attested British leader and one who was prominent in the second half of the fifth century. The Breton material certainly gives Riothamus a good excuse for being in Britain, so perhaps they were one and the same person (and see Arthur the King via the sidebar link).

Geoffrey of Monmouth's History of the Kings of Britain may even mention Riothamus, confusing and combining him with the deeds of Arthur. Geoffrey spends a good deal of time recounting Arthur's conquest of Gaul but most scholars write this off as a flight of fancy (unusual in a work which attempts to stick to traditional or historic events, even if it is prone to flights of apparent fancy in the way it relates those events).

Geoffrey's Gaulish episode can be tied to the reign of Leo I of the Eastern Roman empire (457-474), and less certain pointers whittle which down to about 469-470. This leads to Riothamus, a genuine and historically-attested British leader who was certainly fighting in Gaul at that time.

A powerful leader

Riothamus was clearly a very important and powerful person in Britain. Even if he cannot be equated with Ambrosius Aurelianus he must still have been one of the more powerful men of his time, powerful enough to devote large resources to rebuilding Cadbury Castle and to leading a sizable force across the Channel to play its part in imperial politics, just as Magnus Maximus and Constantine III did before him. Unfortunately, his own expedition was just as unsuccessful, and probably drew away vital resources from Britain's own defences [3].

Did those defences suffer as a result? Possibly, because in 477 we have a powerful Saxon warlord in the form of Ælle landing on the south coast, someone important enough to immediately claim the title of bretwalda.

Over the course of about fifteen years he carved out his own kingdom, which probably means that his warband faced determined resistance all the way, but more importantly, it seems highly likely that he was the overall authority behind the campaign which would have pushed westwards along the Thames Valley and ended up at the siege of Mons Badonicus. In the end, he was defeated and sank into obscurity (or was killed), but it was probably a near-run thing. Perhaps Riothamus' 12,000 troops could have prevented him from even landing in Britain in the first place.

The disappearance from history of Riothamus does not rule out the possibility of him successfully returning to Britain, but this would also be a reasonable date for a replacement to take command of Britain's defence as his successor. Arthur, perhaps.

Romano-British warrior

Picturing any Briton during the murky events of the fifth century is fraught with problems, but Riothamus was probably Christian, at least nominally, bilingual in Latin and Brythonic, literate, and with something of a classical education. He probably dressed in the Late Roman military costume typical of any leader of his time when on campaign, and probably had a personal following of cavalry, a comitatus in the Early Welsh and Late Roman practice, much as Arthur is thought to have had.

Cadbury Castle
Even today, Cadbury Castle presents the image of a powerful and defensible location, with views across the whole of Somerset giving it a level of strategic importance

[3] It could be argued that, despite his execution after five years as Western Emperor, the plans of Magnus Maximus were a great success, if only because he ordered the foundation of two military bases: Armorican Brittany and Galician Britonia. From the former came the armies which (re-)conquered Britain in 1066, and the latter repelled the Moors and initiated the Reconquista.

Linking Riothamus to Cadbury Castle is not idle speculation. This Iron Age hill fort was reoccupied in the mid-fifth century and was massively refortified. The work was clearly organised by a very important and powerful British leader, probably in the 460s. The site had been a British Masada in the first century, the scene of an heroic last struggle by elements of the Durotriges tribe, and this memory probably survived into the fifth century.

Its reoccupation was not in the form of a city or an established seat of government for successive rulers. Instead it seems to have been a place which a British leader of stature could make his personal headquarters. This leader probably had links to the Dumnonian aristocracy, thanks to the hill fort's location within that kingdom's territory, so perhaps it was the Dumnonian king who was responsible for the work rather than an over-king.


So was Riothamus, 'rigotamus', the 'supreme king', the same person as Ambrosius Aurelianus or, as has also been claimed, Arthur?

Given the timeline which has been calculated here for the British leaders of post-Roman Britain (see link in the sidebar), it seems more likely that he could be equated with Ambrosius rather than Arthur, but others have certainly considered it possible that he was Arthur.

A Breton writer of around the eleventh century certainly thought so when he sketched out the period and recounted the events of the Gallic War of the 460s. It is also quite possible that Riothamus fought some of the twelve battles which were later given to Arthur. Even Geoffrey of Monmouth, drawing on an older work (or works) thought so.

As usual with this period, nothing is straightforward. The real Riothamus fought his campaign during the reign of Leo, advancing to the neighbourhood of the Burgundians, and his line of retreat in 470 shows him moving towards the real Burgundian town of Avallon.

Where he has no recorded death.

Meaning that he could live on as a 'once and future' king in myth and legend.


Main Sources

Ashe, Geoffrey - The Landscape of King Arthur, Guild Publishing, London, 1987

Jordanes, Cassiodorus - The Origin and Deeds of the Goths, Dodo Press, 2007

Salway, Peter - Roman Britain, Oxford History of England, Oxford University Press, 1981

Other Sources

Edward Dawson - Conversations on name construction

Geoffrey Tobin - Provided Note 3, in the sidebar



Images and text copyright © P L Kessler. An original feature for the History Files.