For my own part, I agree with those who think that the tribes of Germany are free from all taint of inter-marriages with foreign nations, and that they appear as a distinct, unmixed race, like none but themselves. Hence, too, the same physical peculiarities throughout so vast a population. All have fierce blue eyes, red hair, huge frames....However, if we look at the people that live in what's now modern-day Germany we can see that red hair is rather uncommon. Either the ancient writers located 'Germany' somewhere different to where we locate it today or the population make-up of Germany has massively changed in the last 2000 years. Either that or the ancient writers were simply mistranslated or wrong.
All these possibilities are interesting in their own way, however there's one other possibility that, although far-fetched, is maybe even more interesting. And that is that these 'ancient' works, far from being truly ancient, were actually medieval/renaissance forgeries. In fact, the authenticity of some of the works of Tacitus were questioned by scholars when they first re-emerged into print after the dark ages.
If that was indeed the case then the next question would be - why create a forgery describing the Germans as red-haired when they clearly weren't?
In previous posts I've talked about the possible relationship between red hair, the Reformation and the colour orange. Namely that red hair and the colour orange became totemic symbols for the Protestant movement.
Now Germany of course was something of a hotbed in regards the Protestant movement. (I've also noted before the common theme of red hair in the Northern Renaissance artwork of the period.) Anyway, could the Reformation/Humanist scholars of the time deliberately have forged 'ancient' works to emphasise the totemic 'red hair' of the Germanic tribes? Much like the way the Nazis repainted the Germanic peoples as being blond-haired and blue-eyed to suit their particular vision.
It should be noted that many of these ancient works tell the story of Rome's Caesar and Co, fighting red-haired tribes in the north of Europe. Paralleling how the Roman Catholic church fought the Protestant northern states of renaissance Europe. Were these works another example of an ancient story being told to parallel and influence a more modern cause? - the same way that Protestants retold the story of ancient Rome's Lucretia as an allegory for the transgressions of the Roman Catholic pope.
It's an interesting idea.