Late Roman Unit Sizes

[Nathan Ross]

Taking your lowest figure of 600 men for a numerus, Constantine’s demand for 300 men from each numerus would mean that Constantine was seriously intent on weakening Julian’s army.

Possibly. Or the numeri he requested in full were only c.600 men, and the rest were 800-1200?

Most likely a standard troop draft anyway. Julian probably did much the same when he assembled his own expeditionary force and marched east.

You write that a numerus “probably comprised c.600-800 men, maybe 1,200 men. For me personally, I want more information, like how many centuries and how many men in a century.

I'm tending to find that Vegetius (II.14) probably had it right - 110 men under one centurion and one standard bearer. This subunit variously referred to as a century, ordo or 'cohort'.

So a numerus auxilium might consist of six subunits (of 110+2 men each) making 672 men. These would be numeri, or arithmoi, like the six that Sozomen mentions being sent to Ravenna. A larger auxilium or a palatine legion might consist of eight subunits (896 men) and a comitatensis or limitanei legion ten subunits (1120 men). In all cases the number could be rounded up for paper strenth, or reduced for operational strength or after the detachment of temporary service units.

Still very hypothetical, but the kind of figures this produces seem to be more or less in tune with the few source estimates we have.

Ammianus mentions seven legions and a number of numerii amounting to 20,000 men were stationed at Amida... I get exactly 20,000 men as per Ammianus, so something is working for me.

No - this is often misquoted. Ammianus (19.2.14) says intra civitatis ambitum non nimium amplae legionibus septem et promiscua advenarum civiumque sexus utriusque plebe et militibus aliis paucis ad usque numerum milium viginti cunctis inclusis - "for within the limits of a city that was none too large there were shut seven legions, a promiscuous throng of strangers and citizens of both sexes, and a few other soldiers, to the number of 20,000 in all."

The version by Clark (c.1911, I think) adds an extra word to make milium centum viginti - 120,000 - and this is sometimes quoted as the original. But Clark was obviously thinking that a legion was c.6000 men. In fact the amendation is unnecessary.

There was only one legion stationed in the city - V Parthica - and the other six had retreated before the Persian advance, having abandoned their positions and/or been defeated. So they almost certainly would not have been at full strength. So if we give V Parthica a full strength of 1200 men, and the others a generous 800 each, we get a figure of 6000 men for the legionary garrison. This is probably still too high. But if so, the remaining 14,000 people would be the inhabitants of the town, refugees ('strangers') and irregular troops.