The 1,000 man legion

[Marcus_Ulpius_Trajanus]

Great stuff, Paul!

I think that this demonstrates that there was a 'comfort level' of force size from 10 to 30k for most Roman campaign purposes---with higher numbers for 'major effort' campaigns meant to settle some question once and for all--Germany in AD15-16 (which didn't work out exactly) and Dacia, and the Jewish revolt of AD66-70 (which did).

Looking back at Robert/Vortigern's list, I think we see something similar: Real big armies to settle the civil wars (Constantine/Maxentius & Constantine/Licinius) and then the major efforts that Julian put out in 363 against Persia, and that failed expedition to recover Africa in 457. That one in particular is interesting from a conter-factual perspective--would a successful recovery of Africa stopped the slide of the Western Empire in any meaningful way?

And back to Tim's original question of whether the Romans used smaller legionary units in the East, it appears that they did, although I do find interesting the composition of the Eastern Field Army: (usually dated to sometime around AD395)

10 Vexillationes comitatenses:
Comites catafractarii Bucellarii iuniores
Equites armigeri seniores Orientales
Equites tertio Dalmatae
Equites primi scutarii Orientales
Equites secundi stablesiani
Equites tertii stablesiani
Equites promoti clibanarii
Equites quarti clibanarii Parthi
Equites primi sagittarii
Cuneus equitum secundorum clibanariorum Palmirenorum

2 Auxilia palatina:
Felices Arcadiani seniores
Felices Honoriani seniores

9 Legiones comitatenses:
Quinta Macedonica
Martenses seniores
Septima gemina
Decima gemina
Balistarii seniores
Prima Flavia Constantia
Secunda Flavia Constantia Thebaeorum
Secunda Felix Valentis Thebaeorum
Prima Flavia Theodosiana

11 pseudocomitatenses:
Prima Armeniaca
Secunda Armeniaca
Equites tertio Dalmatae
Fortenses auxiliarii
Funditores
Prima Italica
Quarta Italica
Sexta Parthica
Prima Isaura sagittaria
Balistarii Theodosiaci
Transtigritani

--The core of the army being a lot of close order infantry--the 9 legio comitatenses, and probably several of the psuedocomitatenses (the prima, quarta and sexta Italica units are almost certainly decended from the Italica legions on the Eastern border) And 4 units of clibanarii/catafracts (to counter the Sassinid clibanarii?)

But if you look at the composition of the border forces, for example, the Dux of Arabia,

Praefectus legionis tertiae Cyrenaicae
Praefectus legionis quartae Martiae
Equites scutarii Illyriciani
Equites promoti Illyriciani
Equites Dalmatae Illyriciani
Equites Mauri Illyriciani
Equites promoti indigenae (split over 2 separate locations)
Equites sagittari indigenae (split over 2 separate locations)
Ala nona miliaria
Ala sexta Hispanorum
Ala secunda Constantiana
Ala secunda Miliarensis
Ala prima Valentiana
Ala secunda felix Valentiniana
Cohors prima miliaria Thracum
Cohors prima Thracum
Cohors octava voluntaria
Cohors tertia felix Arabum
Cohors tertia Alpinorum

Its probable that all of these units are not 'up to strength' but the large number of cavalry units under the border dux would indicate to me that there is a lot of patrolling going on.

All of this says to me that here at least the field army is back up force for border problems.