The influence of the Roman army on the military

[Sean Manning]

Looking through the dictionary it seems all the military ranks were derived from Latin, though I admit, this is not really a direct influence of the Roman army. Military terms such as military, medic, defilade, enfilade, etc are also derived form latin.
Vincent

Checking a dictionary with etymologies is a good idea, but if you look more closely you will see that most of them entered English through French. This is because there was no existing jargon, and French culture was very prestigious at the time, so the English copied French words.

The Greeks, Macedonians, and Romans were a major influence on the development of modern armies, but so were many other things. The armies of 15th century Europe had a lot to contribute too.