Greatest Expansion of the Roman Empire - When?

[Tiberius Clodius Corvinus]

I see it as a gathering of the tribes, including, as you say the old, young, and women.....

Wouldn't this mean the whole of their land had been left entirely depopulated? And fabulously easy to conquer even it would've been no use to Rome :?
I'd sooner think the numbers are drastically exaggerated.
(Btw, same seems to be the case with Germania, then sometimes numbers of warriors are stated, that never could've lived of the land.)