Late Roman Unit Sizes

[Frank]

Going back a little to this thread, I'd still say that there is no evidence from the principiate period (for which we have far more epigraphic and literary detail) that legionary cohorts were commanded by anybody!

In the later empire, both 'tribune' and 'cohort' seem to shift in meaning (along with 'legion' and most other things...), and we have tribunes commanding legions, numeri of auxilia and old-style cohorts...

This is an important point! The command structure changed dramatically once in the 4th century, even if starting in the 3rd century already.

In the principate the story-book structure was:

provincia - exercitus legati augusti pro praetore

sector (of a province) - legion plus attached cohorts/alae commanded by a legatus legionis. And this is not a legion. This is a small exercitus with a legion as its core!

tactical unit - auxilia cohorts/alae commanded by tribunes/praefects and vexillationes of the legion commanded by tribunes.


In the late empire the legatus legionis disappears and was replaced by the praefectus legionis. But also the command structure changes. The structure is now:

praefectura or region: exercitus commanded by a magister militum or a comes

sector: exercitus of a front sector commanded by a dux (sometimes comes)

tactical unit: all kinds of units, e.g. cohorts, alae, numeri, legions comanded by tribunes, praefecti and praepositi.


You see what happened? The legion moved to the same level as a the former auxilia cohort. You should also consider, that the entire civil administration was not longer the responsibility of the legion. Also parts of military logistics was gone to the central fabricae and the now civil primipili dealing with the annonae militaris and supply of the military. There was no need anymore for a big legion with a big staff for military and civil administration and logistics.


The legion was now just an ordinary tactical military unit, led by a praefect or a tribune reporting to the commander of the exercitus, a magister militum, comes or dux. We also know not that much about the sub-structure of the late roman legion. If the commander was just on the level of a tribune, regardless if he was called praefectus if limitanei, he should command centurions now. And he needs just a small staff like a former tribunis cohortis: a cornicularius tribuni, a beneficarius tribuni and a few librarii, even if the titles and ranks of the NCOs changed too. The local administrative work was always done by the signifers of the centuriae anyways.


But, if the commander of a cohort and the commander of a legion are of same rank and fullfill the same role, because all former additional functions of the legion were stripped off in the late roman army, the units they are commanding should be organized similarily and be of comparable size.


Therefore I would not be surprised, If we find a papyrus showing a legio with a confirmed paper strength (!) of around 500 men (480 plus some staff and officers). The unit is still called legio, because it emerged from a vexillatio legionis hundred years ago. Tradition had always a strong meaning in the roman military. Heck, they still used terms like hastatus or pilus hundreds of years after it lost its meaning. Other vexillationes legionis were renamed, by whatever reason. Also 800+ men sounds reasonable, if the other way around a legion was stripped off any cohorts but the 1st cohort by vexillationes sent to campaigns and never came back.