Flavius Claudius Constantinus known as Constantine III (1). The last of a series of British supported usurpers to the imperial throne of the Western Roman Empire.

At the end of 406 AD an army of assorted Germanic tribes moved across the frozen Rhine, defeated a force of Franks and moved into Gaul; it was feared that they would cross to Britain.

The Roman Army in Britain revolted, and following the pattern set by Magnus Maximus selected a series of usurpers as imperial candidates. First Marcus, then Gratius were chosen, and when found wanting by their masters, discarded. Their choice then fell on one Constantine; his origins are obscure, Edward Gibbon says that he was only a "private soldier". Nevertheless, in 407 AD the Army proclaimed him imperator and he immediately led an invasion force across to the continent. The legions based in Gaul switched their allegiance to him and Constantine seems to have reached some sort of agreement with the invading tribes. Sufficient to enable him to claim Gaul as his own by 408 AD, when he occupied Arles. (Which had by now replaced Trier as the headquarters of the Gallic prefecture.)

At which point it should be noted that whatever the extent of the troop withdrawals previously effected by Magnus Maximus and Stilicho, that the army in Britain still felt sufficiently confident in its own strength to take on both the barbarian invaders and the forces of Honorius, the legitimate Emperor of the Western Roman Empire.

With Gaul under control Constantine sent Gerontius to invade Iberia and put down an uprising by some of Honorius’ Iberian relatives. Like Magnus Maximus before him, Constantine now ruled a northern-western Empire that stretched from Iberia to Britain. (A task, it must be said that had been made somewhat easier by the murder of Stilicho in 408 AD, which removed the ablest military commander in the west.) Honorius was forced to recognise Constantine's authority, and shared the consulship with him in 409 AD .

But later that year Constantine's empire began to unravel. First Britain, then much of northern Gaul revolted, and when Constantine sought to replace Gerontius with his son Constans, Gerontius revolted in turn and acclaimed one Maximus as emperor, and moved his forces into Gaul and laid siege to Arles.

Honorius response was to gather an army under the command of one Constantius (2), who advanced into Gaul in 411 AD, defeated Gerontius, and besieged Constantine in Arles. Constantine lost hope, took refuge in a church and was ordained, perhaps thinking that this would save him. It did not, he was soon captured and beheaded.

(1) History seems to refer to him as Constantine III despite his status as an usurper, but he should not be confused with the other Constantine III, who was briefly emperor of the Eastern Roman Empire in 641 AD or even the Constantine III who was King of Scotland in 995-997 AD.)

(2) this would be the Constantius who later become the emperor Constantius III in AD 421.

Part of the Sub-Roman Britain project, where sources are detailed.

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