Blowhard, Esq. writes:

Because the military position of the imperial government in the fifth century was weak, and because the Germanic invaders could be appeased, the Romans on occasion made treaties with particular groups, formally granting them territory on which to settle in return for their alliance. Four such agreements were recorded in fifth-century Gaul: with the Visigoths, who were given part of Aquitaine, in 419; with the Burgundians, settled on the upper Rhône near Lake Geneva in about 443; with a group of Alans, granted ’empty lands’ around Valence in about 440; and with another Alan group some two years later, settled in an unspecified part of northern Gaul.

In recent scholarship these treaties have received a disproportionate amount of attention, and have been paraded as evidence of a new-found spirit of cooperation between incoming Germanic peoples and the Romans, both those at the centre of power and those in the provinces. But is it really likely that Roman provincials were cheered by the arrival on their doorsteps of large numbers of heavily armed barbarians under the command of their own king? To understand these treaties, we need to appreciate the circumstances of the time, and to distinguish between the needs and desires of the local provincials, who actually had to host the settlers, and those of a distant imperial government that made the arrangements.

I doubt very much that the inhabitants of the Garonne valley in 419 were happy to have the Visigothic army settled amongst them; but the government in Italy, which was under considerable military and financial pressure, might well have agreed to this settlement, as a temporary solution to a number of problems. It brought an important alliance at a time when the imperial finances were in a parlous condition. At the same time it removed a roving and powerful army from the Mediterranean heartlands of the empire, converting it into a settled ally on the fringes of a reduced imperial core. Siting these allies in Aquitaine meant that they could be called upon to fight other invaders, in both Spain and Gaul. They could also help contain the revolt of the Bacaudae, which had recently erupted to the north. It is even possible that the settlement of these Germanic troops was in part a punishment on the aristocracy of Aquitaine, for recent disloyalty to the emperor. …

The interests of the centre when settling Germanic peoples, and those of the locals who had to live with the arrangements, certainly did not always coincide. The granting of some Alans of lands in northern Gaul in about 442, on the order of the Roman general Aetius, was resisted in vain by at least some of the local inhabitants. ‘The Alans, to whom lands in northern Gaul had been assigned by the patrician Aetius to be divided with the inhabitants, subdued by force of arms those who resisted, and, ejecting the owners, forcibly took possession of the land.’ But, from the point of view of Aetius and the imperial government, the same settlement offered several potential advantages. It settled one dangerous group of invaders away from southern Gaul (where Roman power and resources were concentrated); it provided at least the prospect of an available ally; and it cowed the inhabitants of northern Gaul, many of whom had recently been in open revolt against the empire. All this, as our text makes very clear, cost the locals a very great deal. But the cost to the central government was negligible or non-existent, since it is unlikely that this area of Gaul was any longer providing significant tax revenues or military levies for the emperor. …

The imperial government was entirely capable of selling its provincial subjects downriver, in the interests of short-term political and military gain. In 475, despite earlier heroic resistance to the Visigoths, Clermont was surrendered to them by the imperial government, in exchange for the more important towns of Arles and Marseille. Sidonius Apollinaris, bishop of Clermont and a leader of the resistance to the Visigoths, recorded his bitterness: ‘We have been enslaved, as the price of other people’s security.’ Sidonius’ opposition to this policy of appeasement proved correct — within a year, Arles and Marseille had fallen back into Visigothic hands, this time definitively.

— Bryan Ward-Perkins, The Fall of Rome and the End of Civilization