miles

Miles, militis is third declension, usually masculine, and a consonant stem, so the genitive plural is militum rather than militium.

Latin is fond of the collective singular here: miles Romanus can mean the entire Roman army, so a singular miles with plural sense is idiom rather than error. The historical trap is the medieval shift. In a classical text miles is the ordinary ranker on foot, the man in the legion. In this corpus, which leans late, miles has become the knight, implying a horse, land and status, and translating it "soldier" there flattens the whole social point. Related: militia, which is military service and not a militia in the English sense, and the verb milito, "to serve as a soldier". English military, militant, militia; French chevalier and Spanish caballero replaced it entirely.