When this fellow Gary H. speaks, I listen. This is exerpt, a mere taste only! from his essay "Battle in the Early Medieval West".
The other problem with the ‘barbarization’ hypothesis is that it is more or less impossible to know what the norms of ‘Germanic’ warfare were before the fifth century. Archaeology gives us some interesting insights here and there about practice, armament and organisation. The Graeco-Roman authors give us other hints but these are so mired in classical ethnographic stereotyping that they are difficult to make use of and seem often to contradict the implications of the archaeology. That apart, the idea of ‘Germanic’ warfare have actually been drawn from the sources of the western European early Middle Ages, after the settlement of Germanic-speakers in the provinces of the Empire. Here the argument, obviously, becomes circular: the nature of early medieval western warfare was ‘Germanic’ because, as we can see in the sources of the period, it conforms to what we know ‘Germanic’ warfare was like; but our idea of what ‘Germanic’ warfare was like is drawn from the sources of the early medieval West. Even the ‘barbarization’ of the Late Roman army can be argued to represent a very Roman process, based around Roman ideas of what barbarians were like, rather than the importing of actual barbarian practices.
This is a very small piece of a very big essay on medieval warfare. Please read it...and let me know what you think. He does not shy away from controversy, and like any GOOD academic, he backs up his opinions with facts.
Please go to his blog to read more. Please.