Late Roman Army - seniores and iuniores

[Nathan Ross]

how about another vexillation being split off afterwards and in turn becoming an independent unit? How would you distinguish that one from the parent unit (your 'seniores') and the first split-off (your 'iuniores')... your system would only allow for the parent unit and the first split-of to be distinguishable as 'seniores' and 'iuniores'.

I would see the 'parent unit' (the original full-size legion) as being distinct from both the 'seniores' detachment and the 'iuniores'. Once they were formed into smaller sized field army units, these new legions were not subdivided (ie all of them remain at c.1000 men)

So, as another example, we have in ND the three legiones comitatensis Septima Gemina, Septimani Seniores and Septima Iuniores: the original VII Gemina would seem to be the 'parent' of all three. Under this theory, a first (double cohort?) detachment from the original legion in Spain would be taken into the field army as the Septimani. At some later date a second detachment of the same size would be drawn from the original legion and named Septimani Iuniores, with the first detachment now assuming the name Septimani Seniores. At a later date still the remains of the original legion, sent to the east, would become the Septima Gemina.

In this case, all three ended up as comitatensis legions. In the majority of cases, however, the detachments gained added status as palatine units of the field army, while the original 'parent' legion became limitanei.

There are also a number of units in the ND called Gallicani (ie Divitenses and Solenses Gallicani) or Iuniores Gallicani (but never Seniores Gallicani!). These might represent further detachments drawn from the original 'parent' at a later date, perhaps to reinforce a depleted western field army. The 'Gallicani' name would distinguish them from the previously-raised Seniores and Iuniores units.

It's complicated to explain, but I think it seems fairly simple in practice and doesn't involve either a radical increase in overall army numbers or a radical decrease in individual unit size. And it's a lot simpler than the idea of all the field army units being split in half and marched this way and that...