The Vexillation

[Frank]

I don't honestly understand where the 2000-3000 man estimate for a Limitanei Legio comes from.

I don't believe in this larger legio limitanei, too. But it is still one of the major theories.

But the size of the late roman legion does not matter. During the principate a vexillatio could have any size, even if 2 cohorts was not uncommon. But just for a detachment of a legion to another exercitus, which is just one of many cases of vexillationes. Perhaps much less common than 5 or 10 soldiers, or any mixed force but not uncommon. It was just the latin word for "detachment" during the principate.

Surprisingly in the late empire the term vexillatio was now reserved for a cavalry unit of perhaps 300-600 men, as far as I know.

So I can't believe, that there is any standard or formula, the size of a vexillatio is based on. Because it was the nature of a vexillatio to be extremely flexible. Same with a numerus. At least during the principate.