Now, I'm no expert on late antiquity (as anybody reading this blog will have guessed), but I'm very excited to read (here) about the archaeological discovery at Kalefeld in Lower Saxony (well over 100 miles east of Cologne) of the wreckage from a 3rd-century Roman-German battle, unknown from historical sources.
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I was a bit taken aback by the broadness of the generalization that "the battle of the Teutoburg Forest, which took place in 9 AD, resulted in the Roman’s Empire withdrawal from Germania without any further attempt to conquer the land beyond the Rhine River again". Even with the Rhine becoming the frontier of regular Roman rule, we've known for some time that Rome was able to project its presence some way beyond the frontier, both economically and militarily. There were six Roman invasions of Germania (including amphibious operations north through Frisia and then south up the Weser) between AD 9 and AD 50 alone (Paul Arblaster, History of the Low Countries (2006), p. 15 - but yes, there are more reputable sources for this and if anybody puts a comment in the box asking for them I'll dig them out). That this sort of thing was still going on in the 3rd century is, I admit, news to me - but there are hints of it in Sigrid Undset's Saga of Saints (tr. E. C. Ramsden, 1934), p. 7 (with reference there to a "Professor Schetelig").