User blog comment:Pacificus Viridis/Gaul Rising/@comment-32656-20120330073102/@comment-4940710-20120331042821

Hmm. Well, I just got through reading the Wikipedia article for each Roman emperor to reign between 235, when Alexander Severus was murdered, and 260. It seems like there was only one major Germanic invasion of Gaul after 235: the Wikipedia articles that I read suggest that the majority of the Germanic invasions that occurred between 235 and 260 were in Dacia, Pannonia, and the Balkans. There was one major invasion of Gaul that took place during the reign of Gallienus, right before Postumus assumed the purple. The participating tribes in that invasion were the Franks, the Alammani, and probably the Juthungi.

Basically, Lordganon, what I'm thinking in terms of is that by the mid-270s, the majority of the citizens of Gaul, Spain, Britannia, Raetia, and the area surrounding Milan have subscribed to a "Two Romes" theory. According to that view, the areas under Postumus' control comprise an internally stable and increasingly prosperous New Rome, distinct from the Old Rome that continued to be plagued by near-constant civil war and frequent Germanic invasions for over a decade. Now since most of the people who live under Postumus' rule think this way, they are not going to particularly care what happens in Pannonia and Noricum (part of the Old Rome), as long as it does not spill over into Raetia (part of the New Rome).

Now as for Rome making similar deals with Germanic tribes prior to the 270s and then screwing them over, how similar is similar? Some of the Wikipedia articles I read mentioned deals relating to tribute that Rome refused to honor (one such renunciation was committed by Philip the Arab). Of course, a promise of being allowed to conquer land is bigger than a promise to pay (increasingly worthless) money. On top of that, even if the Germanic tribes do decide they have good reason to trust Postumus, an invasion by them could be made more difficult, or perhaps even fail, if Aurelian decides to completely pull out of Gaul and/or Spain. Then Postumus (or any successor of his) would be stuck with a serious liability. I'll have to think about that and do some more reading.