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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 had to stay in Italy to fight off another, deeper penetration by the barbarian chieftain, Radagaisus.

c.405 - 415

Aurelius Ambrosius joins the Roman senate.


In early January, 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 necessitated a Roman attempt to regain authority in parts of the old British diocese. Similar attempts were 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," 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. . ."


With both Roman legions withdrawn, Britain endures devastating attacks by the Picts, Scots and Saxons.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 were settled on the east coast as foederati, strengthening the numbers already there.

[1] This event marks the beginning of Post-Roman Britain.

c.410 - 425

Aurelius Ambrosius is the official representative of Honorius to 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 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 "Hallelujah" victory in Wales.

c.432 - 436

Decision of council, led by Aurelius Ambrosius, to confirm the Irish Deisi 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 were they would be lightly supervised. The Deisi have already been settled for some time and would be self-supporting.

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

c.433 - 438

Birth of Aurelius Ambrosius Aurelianus. His mother is probably of British descent and 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 Vortigern. Battle of Cat Guolph (Guolloppum, Wallop in Hampshire). Probably followed by a period of civil strife in eastern and southern Britain.

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 cause, the failure of British to supply provisions. Flow of provisions may have been reduced to nil as a consequence of 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 and Categirn. Four major engagements and several minor ones take place. Categirn and Horsa are killed in the fighting in 455.

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 Aetius, 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 Aetius has his hands full with Attila the Hun.


Second visit of St Germanus to Britain (this time accompanied by Severus, Bishop of Trier). Was this visit spiritually motivated, to combat a revived Pelagian threat or was Germanus sent in Aetius' stead, to do whatever he could 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 were left in peace, for a brief time.


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


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

The most likely interpretation is that Hengist and Horsa really did land at this time. This can be taken as a reinforcement of the existing foederati who caused so much trouble a decade before. Either Hengist was a tribal leader come to take command of his peoples' already established east coast settlements, or he was an opportunist who saw 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 never heard from again.


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

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. Ambrosius is recognised as High King by much of Britain. Assistance of the "warlike Arthur" in the latter part of his reign, who commands 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 westward, 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 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 first Bretwalda, probably in reply to the British High Kingship.


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 have claimed 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 battle of Mercredesburne. 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 form the West Saxons.


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

c.496 - 550

Following the victory at Mount Badon, the Saxon advance is halted with the 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, King of Dumnonia, is killed. Arthur is mentioned in a Welsh poem commemorating the battle.

Cerdic begins to move inland and defeats British king 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 England.


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.