St.Athanasius 500 soldiers reference?

[Nathan Ross]

He may have been Dux Thebaidos

Syrianus was probably dux Aegypti et Thebaidos utrarumque Libbyarum (see AE 1889, 00152 / AE 1934, 00007 and 00008 / AE 2004, 01636) - this was apparently the commander of all the troops in the area before the creation of the diocese of Egypt in c.390 - just as the letter says, 'all the legions of soldiers throughout Egypt and Libya'.

Oddly, somebody called Lucifer of Cagliari describes Syrianus as Iudaeorum militum ducem - perhaps, as an extreme sectarian, this Lucifer referred to all Arians as 'Jews'?

an inscription of a dux commanding two legions:

Circa AD 300... Traianus Mucianus...

Mucianus is one of the earliest known protectores, and his career is usually assumed to begin under Gallienus and extend through to Aurelian or perhaps even Diocletian. Late 3rd century anyway - he's also one of the last known primipili, I think.

The institution of the dux as a frontier or provincial commander seems to date to the tetrarchy (the earliest known one appears in an inscription under Constantius I). So Mucianus's ducate would probably be similar to the 2nd-3rd century model known elsewhere - a senior centurion or primipilare given temporary command over a combined force of varying size for the duration of a particular campaign.