Editing Roman Britain (section)

=== Fourth century history ===
{{See also|Great Conspiracy}}
[[File:Roman.Britain.towns.villas.jpg|thumb|300px|4th century Roman towns and villas]]
[[File:Britain.4th.century.Roman.infrastructure.jpg|thumb|300px|4th century: Degree of Romanisation]]

Emperor Constantius returned to Britain in 306, despite his poor health, with an army aiming to invade northern Britain, the provincial defences having been rebuilt in the preceding years. Little is known of his campaigns with scant archaeological evidence, but fragmentary historical sources suggest he reached the far north of Britain and won a major battle in early summer before returning south. His son Constantine (later [[Constantine the Great]]) spent a year in northern Britain at his father's side, campaigning against the [[Picts]] beyond [[Hadrian's Wall]] in the summer and autumn.<ref>Barnes, ''Constantine and Eusebius'', 27, 298; Elliott, ''Christianity of Constantine'', 39; Odahl, 77–78, 309; Pohlsander, ''Emperor Constantine'', 15–16.; Mattingly, 233–234; {{Harvp|Southern|2012|pages=170, 341}}.</ref> Constantius died in [[York]] in July 306 with his son at his side. Constantine then successfully used Britain as the starting point of his march to the imperial throne, unlike the earlier usurper, Albinus.

In the middle of the century, the province was loyal for a few years to the usurper [[Magnentius]], who succeeded [[Constans]] following the latter's death. After the defeat and death of Magnentius in the [[Battle of Mons Seleucus]] in 353, [[Constantius II]] dispatched his chief imperial notary [[Paulus Catena]] to Britain to hunt down Magnentius's supporters. The investigation deteriorated into a [[witch-hunt]], which forced the ''{{Lang|la|vicarius}}'' [[Flavius Martinus]] to intervene. When Paulus retaliated by accusing Martinus of treason, the ''{{Lang|la|vicarius}}'' attacked Paulus with a sword, with the aim of assassinating him, but in the end he committed suicide.

As the 4th century progressed, there were increasing attacks from the [[Saxons]] in the east and the [[Scoti]] (Irish) in the west. A series of forts had been built, starting around 280, to defend the coasts, but these preparations were not enough when, in 367, a general assault of Saxons, [[Picts]], Scoti and [[Attacotti]], combined with apparent dissension in the garrison on Hadrian's Wall, left Roman Britain prostrate. The invaders overwhelmed the entire western and northern regions of Britannia and the cities were sacked.<ref>{{Cite book |last=Hughes |first=Ian |title=Imperial Brothers: Valentinian, Valens and the Disaster at Adrianople |date=2013 |publisher=Pen & Sword Military |isbn=978-1-8488-4417-9 |page=59}}</ref> This crisis, sometimes called the Barbarian Conspiracy or the [[Great Conspiracy]], was settled by [[Count Theodosius]] from 368 with a string of military and civil reforms. Theodosius crossed from Bononia ([[Boulogne-sur-Mer]]) and marched on Londinium where he began to deal with the invaders and made his base.<ref>Ammianus Marcellinus, Res Gestae 27.8.6</ref> An amnesty was promised to deserters which enabled Theodosius to regarrison abandoned forts. By the end of the year Hadrian's Wall was retaken and order returned. Considerable reorganization was undertaken in Britain, including the creation of a new province named Valentia, probably to better address the state of the far north. A new [[Dux Britanniarum]] was appointed, Dulcitius, with Civilis to head a new civilian administration.

Another imperial usurper, [[Magnus Maximus]], raised the standard of revolt at [[Segontium]] ([[Caernarfon]]) in north Wales in 383, and crossed the [[English Channel]]. Maximus held much of the western empire, and fought a successful campaign against the [[Picts]] and [[Scoti|Scots]] around 384. His continental exploits required troops from Britain, and it appears that forts at Chester and elsewhere were abandoned in this period, triggering raids and settlement in north Wales by the Irish. His rule was ended in 388, but not all the British troops may have returned: the Empire's military resources were stretched to the limit along the Rhine and Danube.
Around 396 there were more barbarian incursions into Britain. [[Stilicho]] led a punitive expedition.
It seems peace was restored by 399, and it is likely that no further garrisoning was ordered; by 401 more troops were withdrawn, to assist in the war against [[Alaric I]].