The "Legion" portrayed in Gladiator should have been, I think, one of the following:
14th Gemina Martia Vitrix (Legio XIIII as opposed to XIV Gemina Martia Vitrix aka the "twinned vitorious at war" and 'the most efficient Legion" which author Stephen Dando-Collins credits with having been in the field with Marcus and:
2nd "Italica" (Legio II Italica)
3rd "Italica" (Legio III Italica)
The latter two have been verifed in several different sources as being Legions (Legiones) specifically raised for Marcus Aurelius' wars against the Germans.
At the end of his book Dando Collins states:
"when actors on the Roman stage had finished their performance they would all come on stage and call to the audience, "Valete et Plaudix" (good bye and applaud us)."
After 4 centuries in service, the 14th's victories ( among them the unnamed fight at "Watling Road" Britain) and defeats ( the debacle of Sabinus & Cotta in Gaul) are Memorable, so perhaps we may say:
Ave Atque Vale (hail and farewell) to the 14th.
These few little paragraphs are the sum total of 250 plus pages on the 14th by Dando Collins and much seemingly unrelated research on my part.