Germanic Urbanisation & Infrastructure Post Augustus

[Nathan Ross]

a notion I have heard repeated that as soon as Rome’s conquests ended so did its supply of slaves, which some people link to its decline and eventual fall.

Yes, I'm not sure how a lack of slaves could lead to 'decline and fall'! I think the usual idea is that slaves were replaced by serf-type labourers, or coloni. But Kyle Harper's Slavery in the Late Roman World, AD 275–425 shows that there were still plenty of slaves in late antiquity.

Supposedly after the defeat of Radagaisus's invasion in AD406 there were so many captives that they collapsed the market and slaves were selling for one solidus (gold piece) each. This suggests that a high demand for slaves existed, and so a prior supply of them must have done too.

Simon MacDowall implies that while the majority of a Germanic warlord or Kings warband were equipped with mail, other types of armour such as iron lamellar influenced by eastern designs...

This may have been true - the Sarmatians seem to have used some sort of armour, although Roman writers like to say it was made of horses' hooves! I don't think there's any evidence of actual lamellar in the west until later.

The only find of body armour in the west from the entire area of 'barbaricum' in the Roman era remains, I think, the Vimose mail shirt. So while there may have been armour in barbarian armies, we have no evidence for it. And, as I mentioned above, Ammianus at least seems to imply that most Alamannic troops were unarmoured (or that's the way I read it anyway!)

...there must have been a huge difference in the economic infrastructure available to Cniva in the 3rd century... Cniva was able not only deploy tens of thousands of Gothic warriors onto Roman soil but defeat a Roman army of 3 legions...

Yes, this is one of the great mysteries of the third century. Where did all these barbarians come from, and how were they so effective? I think we should take all estimates of army sizes with a big pinch of salt - particularly for 'barbarian' armies. It's extremely unlikely that Cniva was able to muster, command or supply an army of that size. But even with an army of less than half the size given in the sources, Cniva's campaign was impressive. Living off the land would have been easy enough inside the empire, however, especially just after the harvest when the granaries were full and virtually unprotected.

Your point about the Marcomannic wars is quite true as well. It does seem that the various 'barbarian' peoples became either more populous, more organised or simply more determined in the later second century and on into the third. But I don't think we need to assume they were necessarily all that different in technology or social structure to previous peoples of the area. Roman armies, as I've said, were far from unbeatable at the best of times, and battles are sometimes won or lost on something like the throw of the dice (aka 'multiple random factors'!)

The old favourite idea about population movements 'pushing' various groups over the Roman frontier might have some truth behind it - Kyle Harper's recent book about the fall of the Roman west more or less resuscitates the notion, with added details about climate change on the Asiatic steppe. Possibly a shortage of natural resources forced the barbarians to start raiding over the border, and the whole thing snowballed?... Or perhaps a pause either in Roman cross-border punitive expeditions or Roman subsidy payments led to a new sense of determination and aggression in barbaricum? Or perhaps the barbarians just became so addicted to Roman produce - and so conscious of their own comparative poverty - that the lure of the empire's easier pickings became eventually too great?