Late Roman Unit Sizes

[Nathan Ross]

Mattock-Wielders (presumably you mean Axemen?) would be Mattiaci would it not?

Aren't you confusing the Mattiaci with the Mattiari?

The latter was a legion - about which we know nothing much beyond the name. The former was a Germanic tribe, located east of Mainz. Mainz-Kastel was still being referred to as kastello mattiacorum as late as the 230s AD, and troops there were called milites mattiacorum. I don't think it unlikely that the original tribe later formed a subgroup of either the Franks or the Alamanni, but either way the name was still in use in the later period for a tribal civitatis.

I think we had a discussion about the Heruli in particular somewhere else.

We did. It's often assumed that there were two groups called the Heruli, either related or coincidentally bearing the same or similar name. One was in the east, the other apparently somewhere near the Rhine. Mythology suggests they were the same people and originated near the Baltic, but beyond that...

Evan, you stated that it is clear a number of units named after tribes were not recruited from those tribes. Can you advise me which ones?

The Sabini and Latini spring to mind - not really recruited from Sabines and Latins, presumably! I don't think Evan was suggesting that we know for certain where they were recruited though...

EDIT - I've mentioned before the early recruit to the Cornuti with an origo in Dacia. Not a tribal name, per se, but it might argue against the particular 'ethnic' origins of auxilia units.