Ancient army numbers

[Marja]

I don't think it's particularly useful to compare military mobilization per male citizen across countries. Citizenship worked differently between Athens and Sparta, let along between Athens, the Delian League as a whole, Sparta, Persia, and the Persian Empire as a whole.

I think it's more useful to compare military mobilization for the total population, including non-citizens, slaves, allies, and subjects. With the other members of the Delian league subsidizing the Athenian navy, it makes sense to consider the entire Delian league as one unit, to consider the Roman Republic and the Socii as one unit, etc. This also reduces statistical noise due to rounding-off army sizes, mis-estimating any one city's population, etc. This assumes that the economic costs of withdrawing so many people from production are more pressing constraints than the total numbers of adult male citizens.

I also think it's important to cross-compare military mobilization between different societies with the same social structures surrounding military mobilization. For example, different societies with feudal systems should have similar mobilization levels, different societies with professional armies with terms above ten years should have similar mobilization levels, and different societies with citizen armies with terms under one year should have similar mobilization levels.

That's leaving aside logistical constraints, which may not be hard limits, on the size of any one field army.