The Danish bog I will have to look up at work on Monday (where my books are) - what I *remember* is that a large number of Roman swords were found, bent so as to be useless, in a bog/old lake, in modern Denmark, way beyond the frontier. I think they are assumed to be spoils of war, dedicated to the gods - but the spoils needn't be 'first-hand' (i.e. taken directly off Romans), they could have reached their resting place in stages.
I have been to the site - but the swords weren't on view, and I now forget its name!