c.410 - Governor Owain Finddu of Glywysing is assassinated in Gwynedd. Irish incursions into Gwynedd, Powys, Garth Madrun, Dyfed & the Gower Peninsula.

411 - Capture, at Arles, of Constatine, last Emperor of Britain. He is executed at Ravenna soon afterward.

413 - The spread of the Pelagian heresy is said to have begun, by Prosper (Tiro) of Aquitaine in his "Chronicle".

418 - The Pelagian heresy is outlawed in Rome.

c.419 - Decurian Tewdrig of Garth Madrun's daughter and heiress, Princess Marchell, marries an aristocratic Irish settler in Wales, Prince Anlach.

420 - In Britain, the Pelagian heresy supposedly enjoys much support from pro-Celtic faction. Pro-Roman Traditionalists support the Roman Church. During this time, according to Prosper, Britain is ruled by petty "tyrants".

c.420 - Death of Coel Hen, probably the last Roman Dux Brittanniarum. The lands of his office in Northern Britain are divided between his descendants and become petty kingdoms of the "Gwyr y Gogledd".

421 - Supposed death of King Gradlon Mawr of Brittany. Probable division of Brittany into sub-kingdoms of Cornouaille and Domnonée.

c.423 - Birth of St. Patrick in Banna Venta Burniae, thought to be near Birdoswald.

425 - Vortigern usurps Imperial power in Britain, possibly as High-King.

c.425 - Cunedda Wledig and his retinue are moved south from Manau Gododdin to Gwynedd in order to expel the invading Irish.

c.425-50 - King Conomor flourishes in Dumnonia, probably from his capital at Castle Dore.

428 - Vortigern invites a number of Germanic warriors to aid him in consolidating his position in Britain. This appears to have been an early use of German mercenaries, who probably settled in the Dorchester-upon-Thames area.

429 - At the request of Palladius, a British deacon, Pope Celestine I dispatches Bishops Germanus of Auxerre and Lupus of Troyes to Britain to combat the Pelagian heresy. While in Britain, Germanus, a former military man, leads the Britons in their 'Hallelujah' victory at Maes Garmon, near Mold on the Welsh border. St. Cadfan founds the Monastery of Barsdey.

c.430 - Death of Tewdrig of Garth Madrun. His British kingdom is taken over by the Irish aristocracy when his son-in-law, Prince Anlach, inherits.

c.434 - St. Patrick is captured by pirates and taken to Ireland as a slave.

435 - Tibatto leads an Armorican movement for independence from Roman Gaul.

c.435 - War breaks out between the Irish settlers in Garth Madrun and Powys. King Anlach of Garth Madrun is defeated and forced to send his son, Brychan, as a hostage to the Powysian Court.

437 - Ambrosius Aurelianus appears as the leader of the Pro-Roman faction in Britain (traditionally returning from exile in Brittany). Vortigern's apparent relative, Guidolin (Vitalinus), fights against Ambrosius at the Battle of Wallop. The latter is probably victorious and is "given all the kingdoms of the western side of Britain".

c.437 - Triffyn Farfog, the Irish chieftain and resident of West Wales, marries, Princess Gwledyr, heiress of the Kingdom of Dyfed.

c.440 - St. Patrick escapes from his captors and returns to Britain.

440 - The Gallic Chronicle records, rather prematurely, that "Britain, abandoned by the Romans, passed into the power of the Saxons." This is probably inspired by Vortigern authorizings the use of Saxon mercenaries, known as foederati, in Britain. They defend the northern parts against barbarian attack and guard against further Irish incursions. The Saxons are given a little land in Lincolnshire.

c.440-50 - King Glywys of Glywysing flourishes in Glywysing.

c.440-90 - King Brychan flourishes in Brycheiniog. His three wives give birth to many saintly children who evangelize Dumnonia.

443 - Death of King Constantine Corneu of Dumnonia. His kingdom is divided between his two sons as Dumnonia and Cerniw.

c.445-50 - A period of Civil War and famine in Britain, caused by the ruling council's weakness and inability to deal with Pictish invasions. The situation is aggravated by tensions between the Pelagian and Roman factions. Semi-desertion of many towns. Migration of pro-Roman citizens toward the West. The country begins to be become divided, geographically, along factional lines.

446 - The Britons (probably the pro-Roman party) appeal to Aetius, the Gaulish Consul, for military assistance in their struggle against the Picts and the Irish. Aetius has his hands full with Attila the Hun and is unable to send any help.

447 - Second visit of St. Germanus (this time accompanied by Severus, Bishop of Trier) to Britain. His visit may have been spiritually motivated to combat a revived Pelagian threat; or possibly he was sent in Aetius' stead, to do whatever he could to help the desperate Britons. Vortigern is accused of incest. Germanus expells the Irish from Powys and restores Cadeyrn's son, Cadell Ddernllwg, to the throne.

c.447 - The Britons, aroused to heroic effort, "inflicted a massacre" on their enemies, the Picts and Irish, and are left in peace for a brief time. Possibly led by St. Germanus.

c.448 - Civil war and plague ravage Britain.

c.451 - During the consulship of Marcian and Valentinian (450-7), Hengest arrives on the shores of Britain with '3 keels' of warriors, and are welcomed by Vortigern. This event later becomes known as the Adventus Saxonum - "the coming of the Saxons".

c.452 - There is increasing Saxon settlement in Britain. Vortigern marries Hengest's daughter, Rowenna, and supposedly offers the Jutish leader the kingdom of Kent. Hengest invites his son, Octha, from Germany with "16 keels" of warriors, who occupy the northern lands, to defend against the Picts. Pictish invasions cease soon afterward.

c.453 - Raids on British towns and cities becoming more frequent. Increasing Saxon unrest.

455 - Prince Vortimer apparently rebels against the pro-Saxon policies of his father, Vortigern, and fights Hengest at the Battle of Derguentid (Crayford). Hengest is victorious and the British army flees back to London.

c.455 - Death of King Clotri of Dyfed. His kingdom is inherited by his son-in-law, Prince Triffyn Farfog, and taken over by his Irish aristocratic relatives.

456 - The indecisve Battle of Rithergabail (Aylesford) in which the rebellious sons of Vortigern, Vortimer and Cadeyrn, defeat Hengest for the first time. Cadeyrn is killed in the fighting.

c.456 - St. Patrick leaves Britain once more to evangelise Ireland. The Saxons call the British nobles to a peace conference at Stonehenge, then turn on them and massacre almost everyone. This is the original 'Night of the Long Knives'.

c.458 - The Saxon uprising is in full-swing. Hengest finally conquers Kent.

c.458-60 - Full-scale migration of British aristocrats and city-dwellers across the English Channel to Armorica, in north-western Gaul. The British contingent may have been led by one Riothamus.

c.459 - Vortigern is burnt to death while being besieged by Ambrosius Aurelianus at Ganarew.

c.460 - Death of King Vortimer Fendigaid of Gwerthefyriwg. He is succeeded by his son-in-law, Ynyr, a minor prince of the House of Dyfed. He changes the Kingdom's name to Gwent, after its capital city of Caer-Gwent (Caerwent).

c.460-70 - Ambrosius Aurelianus, from the pro-Roman faction, takes full control of Britain, leading the Britons in years of back-and-forth fighting with Saxons. The British strategy seems to have been to allow Saxon landings and to then contain them there.

464 - Supposed death of the legendary King Aldrien of Brittany.

465 - Battle of Lapis Tituli (Richborough alias Wippedsfleet), in which the Britons defeat the Saxons, but with great slaughter on both sides. The latter are confined to the Isle of Thanet and there is a respite from fighting "for a long time."

c.465 - High-King Arthur probably born around this time. Birth of St. Dyfrig also.

c.466-73 - A period of minimal Saxon activity. Re-fortification of ancient hillforts and construction of the Wansdyke possibly take place during this time.

c.469 - The 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 Breton force as Riothamus. The bulk of the British force is wiped out in battle against Euric, the Visigothic King, and the survivors, including Riothamus, vanish and are never heard from again.

c.471 - The army of King Ceretic of Strathclyde raids the Irish Coast and carries off some of St. Patrick's new flock and sells them into slavery. The King receives a written reprimand from the Irish Evangelist.

473 - The men of Kent, under Hengest, move westward, driving the Britons back before them "as one flees fire."

c.475 - Death of King Gwrast Ledlwm of Rheged. His kingdom is divided between his sons: Meirchion Gul retains the central Rheged homeland and Masgwid Gloff becomes King of Elmet. The death of King Mor of Greater Ebrauc occurs around the same time. He is succeeded by his son, Arthwys, who probably takes the opportunity to seize the Peak District from Elmet.

477 - The Saxon chieftain, Aelle, lands on the Sussex coast with his sons. The Britons engage him upon landing but his superior force besieges them at Caer-Anderida (Pevensey) and drives them into the Weald.

477-486 - Saxon coastal holdings are gradually expanded in Sussex.

c.480 - Traditional ascendancy of Arthur to the High-Kingship of Britain. King Erbin of Dumnonia abdicates in favour of his son, King Gerren Llygesoc. Death of King Glywys of Glywysing. His kingdom is divided into Gwynllwg, Penychen, Gorfynedd, Edeligion and others.

c.485 - Birth of St. Samson.

c.485-96 - Period of King Arthur's "twelve battles" during which he gains a reputation for invincibility.

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

c.487 - Birth of St. David.

c.490 - Hengest dies. His son, Aesc, takes over and rules for 34 years. Death of Einion Yrth of Gwynedd. His kingdom is divided into Gwynedd and Rhos. St. Cybi Felyn is born in Callington in Cerniw. Death of King Cinuit of Strathclyde. The major portion of his kingdom is inherited by his eldest son, Dumnagual Hen. Galwyddel & Ynys Manaw, however, become independent under the rule of his younger son, Tutgual.

493 - Death of St. Patrick, in Glastonbury according to local legend. Down Patrick seems more likely.

c.495 - The Germanic King Cerdic and his son, Cynric, land somewhere on the south coast, probably near the Hampshire-Dorset border. Their followers establish the beginnings of the Kingdom of Wessex. King Gwynllyw of Gwynllwg carries off Princess Gwladys of Brycheiniog. War between the two kingdoms is narrowly avoided by the intercession of the legendary King Arthur. The couple marry.