Gerontius

Constantine III occupies Arles and established tenuous authority over Gaul, sharing control with marauding "barbarians".

This is generally seen as the beginning of Rome's withdrawal from Britain.

Constantine's two generals Iustinianus and the Frank Nebiogastes, leading the vanguard of his forces, are defeated in 407 by Sarus, Stilicho's lieutenant, with Nebiogastes being first trapped in, then killed outside, Valence.

However, Constantine sends another army headed by Edobichus and Gerontius, and Sarus is forced to retreat into Italy, needing to buy his passage through the Alpine passes from the brigand Bagaudae, who control them.

Constantine secures the Rhine frontier, and garrisons the passes that lead from Gaul into Italy.

Constantine, joined by Roman legions from Spain, has by May 408 made Arles his capital, where he appoints Apollinaris, the grandfather of Sidonius Apollinaris, as prefect.

In the summer of 408, as the Roman forces in Italy assemble to counterattack, Constantine has other plans.

Hispania is a stronghold of the House of Theodosius and loyal to the ineffectual emperor.

Fearful that several cousins of the emperor Honorius will organize an attack from that direction while troops under Sarus and Stilicho attack him from Italy in a pincer maneuver, Constantine strikes first at Hispania.

He summons his eldest son Constans from the monastery where he is dwelling, elevates him to caesar, or junior emperor, and sends him with the general Gerontius towards Hispania.

The cousins of Honorius are defeated without much difficulty and two—Didymus and Theodosiolus—are captured, while two others—Lagodius and Verianus—manage to escape to safety in Constantinople.

Constans executes the two captives and leaves his wife and household at Saragossa under the care of Gerontius to return to report to Arles.

The tribes that had overrun the Rhine defenses in 406 and spent the intervening years burning and plundering their way through Gaul, have reached the Pyrenees, where, led by king Gunderic, they break through Constantine's garrisons and enter Hispania in September 409.

While Constantine prepares to send his son Constans back to deal with this crisis, word comes that his general Gerontius has rebelled, raising his own man as co-emperor.

The remaining forces in Spain, further reduced by the removal of soldiers to fight in the civil war that follows the attempt by Constantine to seize power from Honorius, are unable to provide much resistance to the Vandals, Alans, Suevi, and Buri, who sweep across the Pyrenees in late 409.

Constantine's magister militum, Gerontius, is able to restore control over the situation in Spain, obtaining for the invading Vandals, Alans, and Suebi imperial permission to settle there, but now revolts against Constantine.

Constantine's control of Britain and Spain is thus lost.

Gerontius has by this time promoted one Maximus (his son, or possibly one of his staff), to the rank of Augustus.

Gerontius now marches into Gaul, leaving Maximus in Spain.

Constantine's response to this tightening circle of enemies is a final desperate gamble: encouraged by the entreaties of Honorius' magister equitum, Allobichus, who wants to replace Honorius with a more capable ruler, Constantine marches on Italy with the remaining troops left to him, crossing the Alps into Liguria.

When he learns of the death of Allobichus, whom Honorius had suspected of treachery, Constantine is forced to retreat into Gaul in the late spring of 410.

He is now faced by troops from Spain who have invaded Gaul under Gerontius, who besieges him in Arles.

Constantine's fear of an attack from Hispania despite his best efforts comes to pass in 411, when Gerontius advances with the support of his barbarian allies.

Constantine's position grows even more untenable; his forces facing the rebel Gerontius are defeated at Vienne (411), where his son Constans is captured and executed.

Constantine's praetorian prefect Decimus Rusticus, who had replaced Apollinaris a year earlier, abandons Constantine, to be caught up in the new rebellion of Jovinus in the Rhineland.

Gerontius traps Constantine inside Arles and besieges him.