Late Roman Unit Sizes

[Nathan Ross]

I think he would have specifically referred to the 300 being detached from legions or auxilia but he does not, which leads me to believe that is because they were taken from another kind of unit.

'Aerulos et Batavos cumque Petulantibus Celtas et lectos ex numeris aliis trecentenos'

The units specifically mentioned here are auxilia - but it's not clear whether the 'other numeri' are also auxilia, or legions, or what.

There's an implication that the four units listed are themselves numeri (as they would have been - all the auxilia units on the Concordia tombstones are numeri).

I would think Ammianus's meaning here is that these four are the only units sent at full strength, with 300-man drafts taken from all the others (whether auxilia or field army legions).