"So the Romans have something on the order of 750,000 adult males liable for conscription, of which some 526,000 are in the band the Romans generally think of as ‘fighting age’ (17-46). That is a staggering figure, though of course the Romans never put that many men under arms at one time: peak roman mobilizations in 212 and 211 are around 185,000 (which is still more than double peak attested Seleucid or Ptolemaic mobilizations)."

(https://acoup.blog/2024/02/16/collections-phalanxs-twilight-...)