End of Roman rule in Britain

In 383, the Roman general then assigned to Britain, Magnus Maximus, launched his successful bid for imperial power,[1] crossing to Gaul with his troops. He killed the Western Roman Emperor Gratian and ruled Gaul and Britain as Caesar (i.e., as a "sub-emperor" under Theodosius I). 383 is the last date for any evidence of a Roman presence in the north and west of Britain,[2] perhaps excepting troop assignments at the tower on Holyhead Mountain in Anglesey and at western coastal posts such as Lancaster. These outposts may have lasted into the 390s, but they were a very minor presence,[3] intended primarily to stop attacks and settlement by groups of Déisi, from Ireland.

Coins dated later than 383 have been excavated along Hadrian's Wall, suggesting that troops were not stripped from it, as once thought[4] or, if they were, they were quickly returned as soon as Maximus had won his victory in Gaul. In the De Excidio et Conquestu Britanniae, written c. 540, Gildas attributed 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.[5]

Raids by Saxons, Picts, and the Scoti of Ireland had been ongoing in the late 4th century, but these increased in the years after 383. There were also large-scale permanent Irish settlements made along the coasts of Wales under circumstances that remain unclear.[6][7][8][9] Maximus campaigned in Britain against both the Picts and Scoti,[10][11] with historians differing on whether this was in the year 382 or 384 (i.e., whether the campaign was before or after he became Caesar). Welsh legend relates that before launching his usurpation, Maximus made preparations for an altered governmental and defence framework for the beleaguered provinces. Figures such as Coel Hen were said to be placed into key positions to protect the island in Maximus's absence. As such claims were designed to buttress Welsh genealogy and land claims, they should be viewed with some scepticism.

In 388, Maximus led his army across the Alps into Italy in an attempt to claim the purple. The effort failed when he was defeated in Pannonia at the Battle of the Save (in modern Croatia) and at the Battle of Poetovio (at Ptuj in modern Slovenia). He was then executed by Theodosius.[12]

With Maximus's death, Britain came back under the rule of Emperor Theodosius I until 392, when the usurper Eugenius made a bid for imperial power in the Western Roman Empire until 394 when he was defeated and killed by Theodosius. When Theodosius died in 395, his 10-year-old son Honorius succeeded him as Western Roman Emperor. The real power behind the throne, however, was Stilicho, the son-in-law of Theodosius' brother and the father-in-law of Honorius.

Britain was suffering raids by the Scoti, Saxons, and Picts and, sometime between 396 and 398, Stilicho allegedly ordered a campaign against the Picts,[13] likely a naval campaign intended to end their seaborne raids on the east coast of Britain.[14] He may also have ordered campaigns against the Scoti and Saxons at the same time,[15] but either way this would be the last Roman campaign in Britain of which there is any record.[16]

In 401 or 402 Stilicho faced wars with the Visigothic king Alaric and the Ostrogothic king Radagaisus. Needing military manpower, he stripped Hadrian's Wall of troops for the final time.[15][17][18] The year 402 is the last date of any Roman coinage found in large numbers in Britain, suggesting either that Stilicho also stripped the remaining troops from Britain, or that the Empire could no longer afford to pay the troops who were still there.[19] Meanwhile, the Picts, Saxons and Scoti continued their raids, which may have increased in scope. In 405, for example, Niall of the Nine Hostages is described as having raided along the southern coast of Britain.[20]

On the last day of December 406 (or, perhaps, 405[21]), the Alans, Vandals, and Suebi living east of Gaul crossed the Rhine, possibly when it was frozen over, and began widespread devastation.[20][22]

As there was no effective Roman response, the remaining Roman military in Britain feared that a Germanic crossing of the Channel into Britain was next, and dispensed with imperial authority – an action perhaps made easier by the high probability that the troops had not been paid for some time.[3] Their intent was to choose a commander who would lead them in securing their future but their first two choices, Marcus and Gratian, did not meet their expectations and were killed. Their third choice was the soldier Constantine III.[23]

Gold coin of Constantine III

In 407, Constantine took charge of the remaining troops in Britain, led them across the Channel into Gaul, rallied support there, and attempted to set himself up as Western Roman Emperor.[20] Honorius' loyalist forces south of the Alps were preoccupied with fending off the Visigoths and were unable to put down the rebellion swiftly, giving Constantine the opportunity to extend his new empire to include Hispania.[24][25]

In 409, Constantine's control of his empire fell apart. Part of his military forces were in Hispania, making them unavailable for action in Gaul, and some of those in Gaul were swayed against him by loyalist Roman generals. The Germans living west of the Rhine River rose against him, perhaps encouraged by Roman loyalists,[26][27] and those living east of the river crossed into Gaul.[28] Britain, now without any troops for protection and having suffered particularly severe Saxon raids in 408 and 409, viewed the situation in Gaul with renewed alarm. Perhaps feeling they had no hope of relief under Constantine, both the Romano-Britons and some of the Gauls expelled Constantine's magistrates in 409 or 410.[29][30][31] The Byzantine historian Zosimus (fl. 490s – 510s) directly 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'.[32]

An appeal for help by the British communities was, according to Zosimus, rejected by the Emperor Honorius in 410 AD. In the text called the Rescript of Honorius of 411, the Western Emperor Honorius tells the British civitates to look to their own defence as his regime was still fighting usurpers in the south of Gaul and trying to deal with the Visigoths who were in the very south of Italy. The first reference to this rescript is written by the sixth-century Byzantine scholar Zosimus and is located randomly in the middle of a discussion of southern Italy; no further mention of Britain is made, which has led some, though not all, modern academics to suggest that the rescript does not apply to Britain, but to Bruttium in Italy.[33][34][35]

Historian Christopher Snyder wrote that protocol dictated that Honorius address his correspondence to imperial officials, and the fact that he did not implies that the cities of Britain were now the highest Roman authority remaining on the island.[36] The idea that there may have been larger-scale political formations still intact on the island has not been completely discredited however.

At the time that the Rescript was sent, Honorius was holed up in Ravenna by the Visigoths and was unable to prevent their Sack of Rome (410).[36] He was certainly in no position to offer any relief to anyone. As for Constantine III, he was not equal to the intrigues of imperial Rome and by 411 his cause was spent. His son was killed along with those major supporters who had not turned against him, and he himself was assassinated.[37]