Has anyone ever documented whether the “Roman” settlements were actually settled by Romans who immigrated from Italy, discharged Roman soldiers who might have been recruited from almost anywhere in the Empire, or simply settlements which took the Roman form because it was a superiour culture in terms of technology, architecture, art, etc?
The Roman army peaked in size during the 2nd Triumvirat; after the defeat of Marc Antony and Cleo VII, Augustus cut the regular army in half, to 28 legions (plus the Praetorian Guard, which was his personal bodyguard, and garrisoned in and near Rome), and doled out long-promised land to the retirees. The army was supplemented by 28 legions-worth of auxiliaries drawn from the provinces and deployed as specialists in their native weapons. The idea was to have a decisive edge over local enemies by the auxiliary matchup, also to co-opt the military capabilities of conquered peoples by absorbing them, commanding them, and moving them someplace where they often didn’t know any local languages.
Anyway, the ideal legion was 5000 troops, plus officers; that adds up to 140,000 regulars, plus 140,000 auxiliary troops. After their term of service (which took on the form of the most productive years of a Roman citizen’s life) many were eligible for land, which generally speaking wasn’t available in Italy. Having the Empire sown with towns made entirely of veterans tended to keep things pretty calm, and other than those who got pissed because this or that emperor was a RINO (Roman In Name Only) and rebelled (that characterized most of the 3rd c AD), they are the reason the western empire lasted so long.
The deterioration was also contributed to by the lack of Romans and even Italians; prosperity and a coherent political structure stretching over the entire Med basin and most of western Europe and then some meant local peace everywhere, and serving in the army as a regular didn’t carry the attraction of civic duty. Also, the “real” Romans and the Italian neighbors declined in numbers for various reasons, mostly low birth rate. By the time of the adoptive emperors, the Roman regular army wasn’t too different (other than weapons and comportment) than the auxiliaries. Essentially, the Roman army was a large foreign force. The emperors themselves came from the provinces and had various semi-Roman or non-Roman ancestry.