Late Roman Field Armies

[Robert Vermaat]

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.

Which was, I think, what Evan said? The ND being drawn up c. 390, after Valens' defeat? 

The original question being about the late Roman field army, this very interesting discussion about vexillations and transfers is nonetheless digressing from that.