Roman Legion in late Antiquity

[Robert Vermaat]

The listing of a Tribunis Cohortis Batavorum in 303 probably refers to the Cohortis Primae Batavorum from Batavis in Noricum, not the Tribe/Auxilia Palatina unit.

As it happens, Batavis/Passau was named after a cohort of Batavi in the first place. I would propose that 'Batavorum' can only refer to the original cohortes Batavorum that were spread out across the empire, originally all recruited from the Batavi tribe. The auxilia were in turn named after the cohots or even with a reference to the original tribe, which we see with other new style units at this time. I don't think they were manned by soldiers from Batavis, or soldiers with an ethnic link to the old Batavi tribe/civitas.

Late Roman nomenclature was probably very mutable, as many officials would have absolutely no clue how the army worked. If Flavius Aetius wrote a treatise on the Roman Army would look very different from if Valentinian III wrote one. (Hence probably in part why Vegetius' treatise was so heavily classicized)

Absolutely. If you look at how the supreme command (magister militum etc etc ) is used in military documantation alone, you understand how easy it is to mix up far more complex names in sources written by civilians.