388 - Maximus occupied Rome itself. Theodosius, the eastern Emperor, defeated him in battle and beheaded him in July, 388, with many of the remnant of Maximus' troops settling in Armorica. The net result to Britain was the loss of many valuable troops needed for the island's defense (the "first migration").
396 - The Roman general, Stilicho, acting as regent in the western empire during Honorius' minority, reorganized British defenses decimated by the Magnus Maximus debacle. Began transfer of military authority from Roman commanders to local British chieftains.
397 - The Roman commander, Stilicho, comes to Britain and repels an attack by Picts, Irish and Saxons.
402 - Events on the continent force Stilicho to recall one of the two British legions to assist with the defense of Italy against Alaric and the Visigoths. The recalled legion, known as the Sixth Victrix, was said by Claudian (in "De Bello Gallico," 416) to be "that legion which is stretched before the remoter Britons, which curbs the Scot, and gazes on the tattoo-marks on the pale face of the dying Pict." The barbarians were defeated, this time, at battle of Pollentia.
405 - The British troops, which had been recalled to assist Stilicho, were never returned to Britain as they had to stay in Italy to fight off another, deeper penetration by the barbarian chieftain, Radagaisus.
406 - In early January, 406, a combined barbarian force (Suevi, Alans, Vandals & Burgundians) swept into central Gaul, severing contact between Rome and Britain. In autumn 406, the remaining Roman army in Britain decided to mutiny. One Marcus was proclaimed emperor in Britain, but was immediately assassinated.
407 - In place of the assassinated Marcus, Gratian was elevated "to the purple," but lasted only four months. Constantine III was hailed as the new emperor by Roman garrison in Britian. He proceeded 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. . ."
408 - With both Roman legions withdrawn, Britain endures devastating attacks by the Picts, Scots and Saxons.
409 - 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.
410 - Britain gains "independence" from Rome. The Goths, under Alaric, sack Rome.
413 - Pelagian heresy said to have begun, by Prosper (Tiro) of Aquitaine in his "Chronicle."
420-30 - Pelagian heresy outlawed in Rome (418), but in Britain, enjoys much support from "pro-Celtic" faction. Traditionalists (pro-Romans) support Roman church. During this time, according to Prosper, Britain is ruled by petty "tyrants."
c.440-50 - Period of civil war and famine in Britain, caused by ruling council's weakness and inability to deal with Pictish invasions; situation aggravated by tensions between Pelagian/Roman factions. Vacated towns and cities in ruin. Migration of pro-Roman citizens toward west. Country beginning to be divided, geographically, along factional lines.
c.441 - Gallic Chronicle records, prematurely, that "Britain, abandoned by the Romans, passed into the power of the Saxons."
c.445 - Vortigern comes to power in Britain.
446 - 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 could be sent, at this time, as Aetius had his hands full with Attila the Hun.
c.446 - Vortigern authorizes the use of Saxon mercenaries, known as foederati, for the defense of the northern parts against barbarian attack. To guard against further Irish incursions, Cunedda and his sons are moved from Manau Gododdin in northern Britain to northwest Wales.
c.447 - Britons, aroused to heroic effort, "inflicted a massacre" on their enemies, the Picts and Irish, and were left in peace, for a brief time.
c.448 - Civil war and plague ravage Britain.
c.450 - In the first year of Marcian and Valentinian, Hengest arrives on shores of Britain with "3 keels" of warriors, and are welcomed by Vortigern. This event is known in Latin as the "adventus Saxonum," the coming of the Saxons.
c.452 - Increasing Saxon settlement in Britain. Hengest 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.
c.453 - Increasing Saxon unrest. Raids on British towns and cities becoming more frequent.
c.457 - Death of Vortigern. Vitalinus (Guitolinus) new leader of pro-Celtic Pelagian faction. Battle of Aylesford (Kent) in which Ambrosius, along with sons of Vortigern, Vortimer and Cateyrn, defeat Hengest for the first time.
c.458 - Saxon uprising in full-swing. Hengest finally conquers Kent, in southeastern Britain.
c.458-60 - Full-scale migration of British aristocrats and city-dwellers across the English Channel to Brittany, in northwestern Gaul (the "second migration"). British contingent led by Riothamus (perhaps a title, not a name), thought by some to be the original figure behind the legends of Arthur.
c.460-70 - Ambrosius Aurelianus takes full control of pro-Roman faction and British resistance effort; leads Britons in years of back-and-forth fighting with Saxons. British strategy seems to have been to allow Saxon landings and to then contain them, there.
c.466 - 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.466-73 - Period of minimal Saxon activity. Refortification of ancient hillforts and construction of the Wansdyke possibly takes place during this time.
c.469 - Roman emperor, Anthemius, appeals to Britons for military help against the Visigoths. Reliable accounts by Sidonius Apolonaris and Jordanes name the leader of the 12,000 man British force, Riothamus. The bulk of the British force was wiped out in battle against Euric, the Visigothic king, and the survivors, including Riothamus, vanished and were never heard from, again.
c.470 - Battle of Wallop (Hampshire) where Ambrosius defeats Vitalinus, head of the opposing faction. Ambrosius assumes High-kingship of Britain.
473 - Men of Kent, under Hengest, move westward, driving Britons back before them "as one flees fire."
477 - Saxon chieftain, Aelle, lands on 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 Sussex.
c.485-96 - Period of Arthur's "twelve battles" during which he gains reputation for invincibility.
c.490 - Hengest dies. His son, Aesc, takes over and rules for 34 years.
c.495 - Cerdic and Cynric, his son, land somewhere on the south coast, probably near the Hampshire-Dorset border.
c.496 - Britons, under overall command of Ambrosius and battlefield command of the "war leader" Arthur, defeat Saxons at the Siege of Mount Badon.
c.496-550 - Following the victory at Mt. 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.501 - The Battle of Llongborth (probably Portsmouth), where a great British chieftain, Geraint, King of Dumnonia, was killed. Arthur is mentioned in a Welsh poem commemorating the battle.
508 - Cerdic begins to move inland and defeats British king Natanleod near present-day Southampton.
c.515 - Death of Aelle. Kingdom of Sussex passed to his son, Cissa and his descendents, but over time, diminished into insignificance.
519 - Kingdom of the West Saxons (Wessex) founded with Cerdic its first ruler.
c.530-40 - Mass migration of Celtic monks to Brittany (the "third migration").
534 - Death of Cerdic. Cynric takes kingship of Wessex.
c.542 - Battle of Camlann, according to Annales Cambriae. Death (or unspecified other demise) of Arthur (according to Geoffrey of Monmouth).