Late Roman Field Armies

[ValentinianVictrix]

I would add a caveat to Evan's answer in that the make up of the field armies may have differed after 378AD when the field army commanded by Valen's was largely destroyed. The Notitia only show's surviving field armies at the time it was drawn up, and even then its estimated that it shows field armies in the East from around 390AD and those in the West to around 420AD, lots of room for missing ones.

Yes, they still sent detachments, and these could vary considerably in size.