High Imperial Roman army vs Late Roman army

[Flavivs Aetivs]

You do realize that the reason why the Vandals et al. crossed into Spain was because they were being pursued by the Western field Army? They did have a temporary free reign in Gaul, but the Army mobilized against them after Constantine III came to Gaul.

Furthermore, those taxes in Gaul were going to the Roman state, the only people settled in Gaul without Roman Authority were the Visigoths, all the rest were under the firm grip of Aetius and his Huns and Alans.

Although the roman army was low on manpower, they were certainly not replaced with Barbarians. The Gallic Field Army was indeed strong. 22,500 men at Chalons is my estimate for the Gallic Army (based on a 2/3 strength of AHM Jones 34,000 in the ND to compensate for paper strength, wounded, sick, deserters, etc.)