360's - Series of attacks on Britain from the north by the Picts, the Attacotti and the Irish (Scots), requiring the intervention of Roman generals leading special legions.
369 - Roman general Theodosius drives the Picts and Scots out of Roman Britain
383 - Magnus Maximus (Macsen Wledig), a Spaniard, was proclaimed Emperor in Britain by the island's Roman garrison. With an army of British volunteers, he quickly conquered Gaul, Spain and Italy.
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").
395 - Theodosius, the last emperor to rule an undivided empire, died, leaving his one son, Arcadius, emperor in the East and his other son, the young Honorius, emperor in the West. At this point the office of Roman Emperor changed from a position of absolute power to one of being merely a head of state.
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.
403 - Victricius, Bishop of Rouen, visited Britain for the purpose of bringing peace to the island's clergy, who were in the midst of a dispute, possibly over the Pelagian heresy.
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.