Late Roman Unit Titles - By Weapon

[Felix]

As for slingers, it is possible that they were only employed in the East because they were only available there. I am not convinced this was so, but the military use of the sling seems to have been as much a cultural choice as a strictly technological one. The military use of the sling had a long tradition in the Middle East (well illustrated by the Assyrians), and further west, the Rhodians and inhabitants of the Balearics made a specialty of it; but other peoples don't seem to have had a taste or aptitude for this. Perhaps the Eastern armies had the easiest time maintaining units of slingers.

On the whole I think you are on the right track. I will add one confusing fact, though: it is entirely possible to construct an army where the administrative units have no correspondance to the fighting arrangements. The English of the Hundred Year's War raised units under the auspices of various nobles, and these units were mixed knights, longbowmen, and (early on) heavy infantry. (see http://www.deremilitari.org/resources/p ... twich1.pdf towards the end of the article). We know from battles like Crecy and Halidon Hill that the English army didn't deploy in mixed units of knights (mounted or not) and archers, but in blocks of one type or the other. Now this is way different from late Rome, but is shows a near total separation between administrative units and fighting units. (or perhaps, the English genius for defying logic hock: )