Late Roman Unit Sizes

[Nathan Ross]

Most of these terms were used interchangeably - Vexillatio becomes both a generic term and a specific regiment in the 4th century. Legion and Cohort were both used generically but were specific regiments.

At the risk of labouring this point ( ) - I don't agree!

Vexillatio was not a generic word - it referred specifically to a cavalry unit of the field army. While certain writers (particularly very late ones like Claudian and Gildas) used 'legion' and 'cohort' to describe units generically, we're talking here about official military nomenclature, not literature.

Numerus was used, it seems officially, to refer to many different types of unit, from legiones to auxilia to equites and scholae. So it could not have referred to a single fixed number of men, unless we assume that all these units were the same size.

It is possible that the numeri of auxilia were originally formed with the same organisation as a cavalry vexillatio or schola - they seem to use what might be a new cavalry rank structure, for some reason - but even so this would not explain why legions were also called numeri in the ND and the Perge inscription.