He crossed into Gaul with his army and killed the Western Roman Emperor Gratian. With Gaul and Britain under his control Magnus Maximus ruled as Augustus - a "sub-emperor" under Emperor Theodosius I.
From this moment, Rome’s presence in Britain began to decline as troops were sent to secure holdings in mainland Europe where Magnus seemed to be concentrating his efforts. Most began to evacuate the north and west of the British Isles. Perhaps Magnus assumed there was no need for the military garrisons. Already the picture of an empire in decline is present. There may have been a few minor camps, but most of Roman Britain remained along the eastern side of the Isle.
Because of coin finds, modern historians believe that Hadrian’s Wall was still garrisoned too. However, it would appear that Britain’s Governor/General Magnus Maximus was too preoccupied in campaigning in Gaul - his ongoing effort to build a mini Empire of his own. He seems to have paid little heed to the needs of Roman Britain during this time. The Isle began to suffer coastal raids along the east. These were from Picts of Caledonia and Saxons from the Germanic areas of mainland Europe. Magnus Maximus ordered Roman troops to be dispatched from Britain to help in his quest to secure his new mini-empire in mainland Europe. He was playing a careful game of politics by pretending to pay homage to the Roman Emperor Theodsius I.
Also, in the West from Ireland; came raids by Scotti to the north-west of Britain (today’s Scotland) and also other Irish raids and settlements into Wales and Cornwall. Britain seems to have been raided by seafarers from all directions while Roman soldiers of Britain were busy fighting in Gaul. These raids seem to have increased when Magnus became absent from Britain. The Isle was marginalised from the grand arena of Europe.
There seems to have been no end to Magnus Maximus and his motivation as newly named sub-emperor Augustus. He gradually tried to gain areas of land here and there within Europe. Eventually. he overstretched. His chance taking and ambitions took one quest too many. He led his army over the Alps to try and gain more power from Imperial Rome. His adventure took him into today’s Croatia where he was defeated by Rome’s forces. He was captured and put to death by Emperor Theodosius in 388 AD.
After Maximus' demise, Britain came back under the direct rule of Emperor Theodosius for another five years until 392 AD. Then a new usurper came along. His name was Eugenius and this person was successful in gaining power off of the Western Roman Empire for two years. Once again Roman Britain seems to have remained isolated with Roman magistrates confined to the eastern towns of Roman Britain. The north and west seem to have continued to be neglected. Meanwhile, in mainland Gaul more internal conflict continued while Britain still suffered foreign sea raids.
Euginius, the new usurper, went the same way as the man before him – Magnus Maximus. Euginius was defeated and killed in 394 AD by Theodosius. For one year Theodosius ruled again over Britain though there was probably no sign of such. Britain was becoming more isolated from the empire with interest continuing to decline. Theodosius died in 394 AD and his ten-year-old son Honorius became Emperor in name. The regent ruler was a man named Stilicho and he was the son in law of the late Emperor Theodosius.
There is a record of a final campaign in Britain by Regent Emperor Stilitcho against the sea raiders. Many historians say this campaign was a naval one. This is believed to be the last Roman Campaign in Britain. This was around 396 to 398 AD.
This was the twilight times of Rome’s influence over Britain and in 401 Rome’s attention was once again diverted from the Isle of Britain as Stilicho faced new wars withVisigoths and Ostrogoths. With the further need of land forces, once again Britain’s Roman garrisons were plundered of manpower. Again the Isles' military ability to defend itself was being taken away. It is possible that Saxon settlements may have started by this time in the South-East and maybe some sort of deal was done to appease these groups. We are now going into a region of history that is becoming clouded with uncertainty. Hadrian’s Wall was abandoned and left to fall into disrepair.
In the New Year of 407 AD, Britain became isolated from Rome again as a new conflict came about in Gaul. More migrating tribes from Eastern Europe crossed the River Rhine and began to wreck the Roman country. These groups of people consisted of Alans, Vandals and Subi. Rome seemed unable to deal with this and Britain was again totally cut off. Roman Britain began to fear that these barbaric tribes might cross the channel and invade the Isle too. Therefore the remaining magistrates of Roman authority were overruled and a new power replaced them. The Roman Britons tried to select new commanders that would take them into the new world that was before them. A way of preserving some of the good that Roman culture had brought Britain needed to be maintained. The civilised world was collapsing around the Romanised Isle. Seafarers were raiding the coastline east and west, The neighbouring land of Gaul was being ravaged by eastern migrating tribes.
Britain’s first choice was two men called Marcus and Gratin who seemed unable to deliver such hoped for security. These men met untimely deaths, but the next choice was Constantine III. He managed to muster the remaining unpaid Romans about Britain and went across the channel into Gaul to counter the eastern migrants that were plundering the land. Another sub -Roman Empire was being carved out of the old and Rome was too busy fighting the Visigoths in Italy to do anything about the new ambitious Constantine III.
In effect, Constantine III was the final lEmperor/Governor/General of Roman Britain but he had also left Britain isolated. This was to peruse conquest of a new Roman dynasty in Europe. In 409 his short-lived empire fell apart. Gauls returned their allegiance to Rome. The rest of his force was in Spain. Also, the German tribes rebelled against him and Britain was still suffering Saxon sea raids.
Because of Constantine’s dire circumstance in Gaul, the Romano-Britons knew they could no longer rely on Rome or petty Emperors for help. In 409 AD Britons expelled all the redundant Roman magistrates from office in towns across Britain. The link with Rome was severed and Britons would now have to try and fend for themselves while Rome began her own battle for survival. The Romano-Britons believed Constantine’s plundering of Roman forces from Britain and his campaigns in Gaul and Spain had left them even more vulnerable. It was because of this that they made the decision to sanction themselves from the old empire and try to build upon what little civilisation they might preserve. In this, they had a final instruction from the Roman Emperor Honorius. He is known to have sent letters of consent that British Isle must fend for herself as best she could.
In 411 Constantine III was assassinated shortly after his son and other supporters were killed. Emperor Honorius was besieged in his new capital of Ravenna. The capital city of Rome fell to the barbaric hordes. Britain was suddenly a very irrelevant and obscure place of little importance to the once grand empire that was in its messy endgame.