Well here is my second guess.

1) Its a Lesser General or Officer.
2) Getai
3) Caius Brittanicus.

I am certain he is Getai because of his helmet showing Thracian and Sarmatian influence. His scale armor also shows Sarmatian influence. The falx have been changed by a sword showing that he must be a command person.

The wild guess is who did this because as I said before I never have paid too much attention to who does this magnificent art. My guess its Caius Brittanicus because of the Hellenic standard bearers, but really I have no clue.

Well hope it is correct.