Bret Devereaux

And you're totally cool with 'milites' covering armed mariners despite the fact that it rarely did in the middle ages?

It means exactly that in some of the Roman sources, which seems relevant to our understanding of the term. Cf. Plaut. Capt. 1.2.61 Angry certainty is almost always unbecoming in a historian.

"Angry certainty" ....yet you're certain that it was used in the way you claim when it's abundantly clear it's not. Which is more probable: unified consistent usage amongst authors who pretended to know more Latin than they did or fragmentation?

In as much as I am staring at the entry in the Lewis & Short which reads "a soldier in sea-service, a marine" yes, I am pretty confident. The thing about a philological question like this is it takes only one example to demonstrate a usage.

The usage in Roman times for sailor was clearly different than what they used for ground pounder or naval infantry. So no unified term then or now. Certainly not by the medieval period.

Er. 1) The term is clearly unified in Plautus and consequently the (small) corpus of old Latin. 2) The Romans certainly do not have a clearly different sense of 'legions on boats' than 'legions on ground.' They have a word for 'rowers' (which is how they might use nautae)...

...but 'rowers' or 'sailors' are not marines. If the question is 'does milites cover sailors in the ancient world' - by and large no? But actually stay tuned for some interesting research by @marquanimous on the Greek context at some point.

They are still militarized. Try telling a modern sailor he's not part of the armed services because he's not naval infantry