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Post-Roman Britain

Chronology of Britain & Ireland

by Peter Kessler, 1 April 1999



The British troops, which had been recalled to assist Stilicho, are never returned to Britain as they have to stay in Italy to fight off another, deeper penetration by the barbarian chieftain, Radagaisus.

c.405 - 415

Aurelius Ambrosius (Ambrosius the Elder) joins the Roman senate.


In early January AD 406, a combined barbarian force (Suevi, Alani, Vandals, and Burgundians) sweeps into central Gaul, severing contact between Rome and Britain. In autumn 406, the remaining Roman army in Britain decides to mutiny. One Marcus was proclaimed emperor in Britain, but was immediately assassinated.

406 /
417 - 420

Most probable period in which Aurelius Ambrosius is appointed consular governor of Maxima Caesariensis. Best chronological fit would be between 417-420, and necessitates a Roman attempt to regain authority in parts of the old British diocese. Similar attempts are made in Armorica and northern Gaul at this time, with varied and intermittent success.


In place of the assassinated Marcus, Gratian is elevated 'to the purple' in Britain, but lasts only four months. Constantine III is hailed as the new emperor by the Roman garrison in Britain. He proceeds to follow the example of Magnus Maximus by withdrawing the remaining Roman legion, the Second Augusta, and crossing over into Gaul to rally support for his cause. Constantine's departure could be what Nennius called 'the end of the Roman empire in Britain...'.

Map of Roman Britain around AD 400
This map attempts to show the political situation in Britannia around the start of the fifth century AD (click or tap on map to view full sized)


With both Roman legions withdrawn, Britain endures devastating attacks by the Picts, Scots, and Saxons


Prosper, in his chronicle, says, 'in the fifteenth year of Honorius and Arcadius (409), on account of the languishing state of the Romans, the strength of the Britons was brought to a desperate pass'. Under enormous pressure, Britons take matters into their own hands, expelling weak Roman officials and fighting for themselves [1].

It seems highly probable that many of the defeated Teutonic raiders are settled on the east coast as foederati, strengthening the numbers already there.

[1] This event marks the beginning of post-Roman Britain, and is covered in depth in The End of Roman Britain.

c.410 - 425

Aurelius Ambrosius is the official representative of Honorius to the British provincial council. 'Wearing of the purple'. Possible failure of effective Roman support during this time.


Pelagian heresy said to have begun, by Prosper (Tiro) of Aquitaine in his Chronicle.

c.418 - 425

Rise of influence and power of Vortigern, culminating in his high-kingship.

420 - 430

Pelagian heresy outlawed in Rome (418), but in Britain it enjoys much support from Vortigern's 'pro-Celtic' faction. Traditionalists (pro-Romans) support the Roman church. During this time, according to Prosper, Britain is ruled by petty 'tyrants'.


Honorius issues a decree forbidding any Pelagians to come nearer to Rome than the one-hundredth mile marker.


Beginning of Vortigern's high-kingship over much of Britain. The provincial council has decided, and external factors dictate, the need for strong, central, leadership. Aurelius Ambrosius can offer no firm alternative.

428 / 429

First use of Saxon foederati and laeti by Vortigern.


At the request of a British deacon named Palladius, Pope Celestine I dispatches bishops Germanus of Auxerre and Lupus of Troyes to Britain to combat Pelagian 'heresy'. The doctrine is supported by Vortigern. Legendary assistance, by St Germanus, in founding of Welsh dynasties in conjunction with Vortigern's sons. While in Britain, Germanus, a former military man, leads Britons to the 'Hallelujah' victory in Wales.

c.432 - 436

Decision of council, led by Aurelius Ambrosius, to confirm the Irish Déisi as commanders of the Demetia area of the west coast to counter the Irish threat. Vortigern acquiesces and assigns Ambrosius 'Dinas Emrys and all the western lands', ie. Ambrosius becomes the architect for the defence of these areas. This is motivated by the council's reluctance to depend entirely on German mercenaries, with their constant demands for increased provisions, especially in an area in which they are to be only lightly supervised. The Déisi have already been settled for some time and are self-supporting.

Traditional dating for the beginning of St Patrick's mission to Ireland.

Cullyhanna dwelling
This is a reconstruction of a typical Irish dwelling in the Bronze Age, at Cullyhanna in County Armagh, and it is probably safe to assume that the Irish in Demetia initially produced dwellings which were similar

c.433 - 438

Birth of Aurelius Ambrosius Aurelianus. His mother is probably of British descent and is considerably younger than Ambrosius the Elder.

c.435 - 437

Delivery of Kent to Hengist and Horsa by Vortigern (possible confusion here with 450). In part for the hand of Hengist's daughter, in part to compensate for the British council's refusal to increase provisions to Vortigern's Kentish foederati.

437 - 438

Open rift between Ambrosius' faction and that of Vortigern. Battle of Cat Guolph (Guolloppum, Wallop in Hampshire). Probably followed by a period of civil strife in eastern and southern Britain.

The Roman city of Bath

Roman Bath, one of the best-known cities which was a neighbour of the provincial capital of Corinum (click or tap on image to read more on a separate page)

440 - 441

German foederati (settled on the east coast and probably enlarged in number since the barbarian raids of 408) take advantage of British unrest and openly revolt, citing as a cause the failure of the British to supply provisions. The flow of provisions may have been reduced to nil as a consequence of the British civil war.


Gallic chronicles report large sections of Britain under German control following Saxon revolt, 'Britain, abandoned by the Romans, passed into the power of the Saxons'. Communications between Britain and Gaul disrupted. Vacated towns and cities in ruin. Migration of pro-Roman citizens towards the west and Armorica begins to gather pace. The country begins to be divided geographically, along factional lines.

441 - 450

British resistance to Saxons under the leadership of Vortigern's sons, especially Vortimer (Gwerthefyr Fendigaid) and Categirn (Cadeyrn Fendigaid (the Blessed)) from their base in the Paganes region. Four major engagements and several minor ones take place. Categirn and Horsa are killed in the fighting in 455.

The River Dee
The River Dee probably formed the border between northern Paganes/Powys and south-western Rheged during the sixth century

442 / 443

Probable death of Ambrosius the Elder, 'who was killed in these same broils', ie. the Saxon revolt. Ambrosius' surviving family is in hiding by now.

An excavation at a site in Gloucester produced an early fifth-century secondary burial in a Roman funerary building with indications that the man was of high rank. Was this Ambrosius the Elder? Considering Ambrosius' son was based in this area, could the family domains have been in this area?


Britons (probably the pro-Roman party) appeal to Aëtius, Roman governor of Gaul, for military assistance in their struggle against the Picts and the Irish (Scots). No help can be sent at this time, as Aëtius has his hands full with Attila the Hun.


Second visit of St Germanus to Britain (this time accompanied by Severus, bishop of Trier). Is this visit spiritually motivated, to combat a revived Pelagian threat or is Germanus sent in Aëtius' stead, to do whatever he can to help the desperate Britons? By this time, the Saxons are contained in some areas by Vortimer.

The Britons, aroused to heroic effort, 'inflicted a massacre' on their enemies, the Picts and Irish, perhaps assisted by St Germanus, and are left in peace for a brief time.


Death of St Germanus in Ravenna. Civil war and plague ravages Britain.

St Germanus of Auxerre
The Alleluia Victory saw St Germanus lead the Britons to a bloodless victory over marauding Saxons, perhaps demonstrating that the country was finally managing its own defence


Traditional date as recorded by Bede and the Anglo-Saxon Chronicle for the Adventus Saxonum, the arrival of Hengist and Horsa in Kent. Obvious conflict with circa 435-437 dates.

The most likely interpretation is that Hengist and Horsa really do land at this time. This can be taken as a reinforcement of the existing foederati who have already caused so much trouble a decade before. Either Hengist is a tribal leader come to take command of his peoples' already established east coast settlements, or he is an opportunist who sees a chance to carve out his own territory in the face of weak native Britons.

c.450 - 451

Probable death of Vortimer. British offensive stalemates.


Increasing Saxon settlement in Britain. Hengist invites his son, Octha, from Germany with '16 keels' of warriors, who occupy the northern lands, to defend against the Picts. Picts not heard from again in this period.


Increasing Saxon unrest. Raids on British towns and cities becoming more frequent.


British betrayal at peace conference. Collapse of British military in east and south of Britain. Vortigern cedes territory to gain his freedom but, despised by all, dies shortly after.

c.455 - 460

The British, lacking strong leadership, are overwhelmed. Saxons raid from Kent to the Severn Valley. Mass migration of British upper class to Armorica.


Aurelius Ambrosius Aurelianus becomes involved in British affairs, organising British resistance. During a period of respite, many British flock to his standard. He initiates a British counter-offensive.

460s - 480s

Extended period of fighting to and fro. Fortification of defensive sites and stationing of troops by Ambrosius. He is recognised as high king by much of Britain. Assistance provided by the 'warlike Arthur' in the latter part of his reign, commanding the mobile field force.


Battle of Wippedesfleot, in which Saxons defeat Britons, but with great slaughter on both sides. Mutual 'disgust and sorrow' results in a respite from fighting 'for a long time'.

c.466 - 473

Period of minimal Saxon activity. Refortification of ancient hill forts and construction of the Wansdyke possibly takes place during this time.


Roman Emperor Anthemius appeals to the Britons for military help against the Visigoths. Reliable accounts by Sidonius Apolonaris and Jordanes name the leader of the 12,000 man British force as Riothamus (of Armorica). The bulk of the British force is wiped out in battle against Euric, the Visigothic king, and the survivors, including Riothamus, vanish, never to be heard from again.


Men of Kent, under Hengist, move westwards, driving Britons back before them 'as one flees fire'.


Saxon chieftain, Ælle, lands on the Sussex coast with his sons. Britons engage him upon landing but his superior force drives them into the forest (Weald). Over the next nine years, Saxon coastal holdings are gradually expanded in the territory of the South Saxons (Sussex).

Ælle apparently takes command of the Teutonic efforts in the south, being acclaimed as the first bretwalda, probably in response to the British high kingship.

Aelle of the South Saxons
The coming of Ælle and his apparently pre-established status as bretwalda spelled eventual defeat and death for the Britons of modern Sussex, and quite possibly led to the siege of Mons Badonicus


Vita Germani, the Life of St Germanus, is written by a continental biographer, Constantius.


Death of Ambrosius. His sons rule small kingdoms in the east and south of Britain. Arthur remains active, and may claim the high kingship.

c.485 - 496

Period of Arthur's 'twelve battles' during which he gains his reputation for invincibility.


Ælle and his sons overreach their normal territory and are engaged by Britons at the Battle of Mercredesburne. The battle is bloody, but indecisive, and ends with both sides pledging friendship.


Hengist dies. His son, Aesc, takes over and rules for 34 years.


Cerdic and Cynric, his son, land somewhere on the south coast, probably near the Hampshire-Dorset border. They eventually control the West Saxons and form an expanding kingdom.


The Battle of Mons Badonicus takes place, presumably under Ælle's command, but perhaps triggered by Cerdic's arrival only a year previously.

c.496 - 550

Following the British victory during the defence of Mount Badon, the Saxon advance is halted with the broken invaders returning to their own enclaves. A generation of peace ensues. Corrupt leadership, more civil turmoil, public forgetfulness, and individual apathy further erode Romano-British culture over next fifty years, making Britain ripe for final Saxon 'picking'.

c.500 - 550

Spread of Celtic monasticism throughout Europe.


The Battle of Llongborth takes place (probably Portsmouth), where a great British chieftain, Geraint, ruler of Dumnonia, is killed. Arthur is mentioned in a Welsh poem commemorating the battle.

Cerdic begins to move inland and defeats British ruler Natanleod near present-day Southampton.


Battle of Camlann, and death of Arthur (some sources say 532). Maeglwn of Gwynedd claims supremacy over British.


Death of Ælle. Kingdom of the South Saxons passes to his son, Cissa, but diminishes into insignificance.


Kingdom of the West Saxons (Wessex) founded with Cerdic its first ruler.

c.530 - 540

Mass migration of Celtic monks to Brittany (the 'third migration').


Death of Cerdic. Cynric takes the kingship of the West Saxons.


Krakatoa explodes with far greater force than the nineteenth century repeat and induces a nuclear winter-effect over much of the globe for the next year or two. Plague soon springs up in Italy and is spread throughout Europe and eventually into Britain.

c.540 - 545

Gildas writes De Excidio Brittaniae, Ambrosius' grandchildren are active: 'His descendants in our day have become greatly inferior to their grandfather's excellence'.


There is plague in Britain, introduced from the Continent. Because the British still have regular contact with the former Roman empire territories, and import many goods through that route, they are much more seriously afflicted than the relatively isolated Saxons.

547 or 549

Death of Maeglwn of Gwynedd.


St David 'takes' Christianity to Wales.

Around this time the Saxon advance is resumed.


Irish monk St Columba founds a monastery on island of Iona and begins conversion of the Picts to Christianity


Probable death of Gildas.


Foundation of the Anglo-Saxon kingdom of Mercia in Engla-land (England).

Tribal Hidage (left) and Grammar of Ælfric (right)
The Tribal Hidage is almost certainly Mercian, although some still argue for a Northumbrian origin, but the British Library version shown here, Harley 3271, is an eleventh century miscellany which includes, amongst others, the Grammar of Ælfric, abbot of Eynsham


The Roman brand of Christianity is brought to Britain for the first time by St Augustine, the missionary sent from Pope Gregory to convert the Saxons. Landing in the territory of the Cantware, the Men of Kent, Augustine founds a monastery and the first church at Canterbury, and is proclaimed its first archbishop.



Text copyright © P L Kessler, adapted from various notes and sources. An original feature for the History Files.