The end of the Roman province of Britannia was a transition from imperial rule and the acceptance of temporary self-government during the 5th century AD, to the sub-Roman period in the centuries that followed.
Britannia was a frontier province in classical antiquity that encompassed large parts of the island of Great Britain after the Roman invasion from AD 43.
The province was governed from the capital of Londinium (London), overseeing territories that covered all of Wales, and stretched from the southern coast of present-day England to Hadrian’s Wall, although during brief periods the border advanced into Caledonia on the Antonine Wall.
Britannia had become an economy partly dependant on military occupation, with an entire industry orientating around the support of military sites and the domestic needs of the soldiers.
In order to maintain security, the province required the presence of several standing legions, but command of these forces provided an ideal power base for ambitious generals and usurpers, that successively threatened imperial rule of the wider empire from the 2nd century AD onwards.
The start of the deterioration of Roman Britain can arguably be attributed to an event known as the ‘Great Conspiracy’ in AD 367, when the Roman garrison on Hadrian’s Wall apparently rebelled and allowed Picts from Caledonia to enter Britannia, around the same time as incohesive waves of Attacotti, Scotti, and Saxons landing on the island’s mid-western and south-eastern borders.
The historian Ammianus Marcellinus described it as a ‘barbarica conspiratio’ that capitalised on a depleted military force in the province brought about by Magnus Magnentius’ losses at the Battle of Mursa Major in Pannonia, after his unsuccessful bid to become emperor.
The invasion placed the province into a year-long state of war, resulting in many of the Romano-British in the western and northern regions murdered, raped, and enslaved, until the invaders were eventually driven back to their homelands.
Further depletion of the province’s military took place in AD 383, when General Magnus Maximus launched a successful bid to usurp the throne from emperor Gratian. Gratian had lost favour because of a perceived favouritism towards the Alans, thus weakening his position and causing his own army to defect to Maximus. Maximus had taken a large portion of the British garrison for his campaign, leaving swathes of territory in the north and west of Britain open to further raids.
In the De Excidio et Conquestu Britanniae, written by the monk Gildas during the sub-Roman period around AD 540, Gildas describes an exodus of troops and senior administrators from Britain to Maximus, saying that he left not only with all of its troops, but also with all of its armed bands, governors, and the flower of its youth, never to return.
During the reign of emperor Stilicho (AD 382–408), Britain’s defences were weakened again when its northern forces garrisoned at Hadrian’s Wall were recalled to campaign against the Visigothic king Alaric, and the Ostrogothic king Radagaisus around AD 402.
Archaeological evidence shows that Roman coinage ceased around this time, suggesting that Stilicho either stripped the bulk of troops in Britannia, or that the Empire could no longer afford to pay those who were still garrisoned there.
In AD 406, Alans, Vandals, and the Suebi crossed the Rhine into Roman territory, leaving Britannia in the precarious position of dispensing its own imperial authority by selecting Flavius Claudius Constantinus (Constantine III) to rule.
Rather than consolidate Britannia’s defences, Constantine declared himself emperor and took the last of the province’s garrisons in an attempt to usurp the sitting emperor, Flavius Honorius. This final act left Britannia unable to defend itself, resulting in the province’s inhabitants rising up in anger and expelling Constantine’s magistrates.
The Byzantine historian Zosimus blamed Constantine for the expulsion, saying that he had allowed the Saxons to raid, and that the Britons and Gauls were reduced to such straits that they revolted from the Roman Empire, ‘rejected Roman law, reverted to their native customs, and armed themselves to ensure their own safety’.
An appeal for help by the remaining inhabitants of Britannia was, according to Zosimus in his text – the Rescript of Honorius of 411, was rejected by the Emperor Honorius in AD 410, around the time that Rome was sacked by the Visigoths under Alaric (although some scholars suggest that the Rescript of Honorius refers to the cities of the Bruttii in modern-day Calabria).
Archaeological evidence suggests that domestic life continued in many major population centres well into the post-Roman period, but gradually became abandoned by the latter 5th century AD.
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