[split] Distances between files and ranks

[Nathan Ross]

You’re adding the 2,000 reservist to the 45,000 men. How can you be sure they are not part of the 45,000 men and should be subtracted?

The text of Civil Wars III.88 seems very clear to me (paying attention to the words and phrases underlined in my quote):

These forces (i.e. the 110 cohorts that made up Pompey's infantry line) amounted to forty-five thousand men, and about two thousand reserves who had come to him from the beneficiaries of his former armies; and these he had distributed throughout the whole force. Seven remaining cohorts he had placed on garrison duty in the camp and the neighbouring forts.

You'd need to check the original Latin very carefully to make sure, but that 'and' certainly appears to mean that the 2000 reserves were additional to the 45,000. The following clause states that the 2000 were mixed with the other troops, giving 47,000 total.

The seven cohorts in the camp and forts were 'remaining', so they are not counted as part of the figure either.

you question me about why would Frontinus round Pompey’s depth, when here you mention “rounding up or down as they saw fit.”

There is a difference, I think, between taking a figure like (say) 24,568 - which might be the very accurate tally of an army's total number on the morning of battle, complied from unit strength reports - and rounding it up to 25,000, or down to 24,000, or saying 'more than twenty thousand' or 'fewer than thirty thousand', and taking a very simple and specific reference to a formation ten men deep and assuming it must really mean eight men deep, because your own calculations tell you that this must be so, and you can't make the numbers work otherwise!