This line is concerning me:
Nulla res melius gesta est quam proelium illud ubi Marius multo minore exercitu multo maiores copias Germanorum in fugam dedit
It's not particularly complex, but the second half of the compound sentence doesn't quite seem right. I translated it as:
No thing (nothing) has been borne more greatly than that (famous yonder) battle, when Marius made the much larger (larger by much) troops of the Germans into flight with a much smaller (smaller by much) army.
The first melius appears to be a comparative adverb, but I would have expected the two armies in the second half to be compared directly against one another rather than the seemingly indirect comparison here.