Amazon Submissive

Xander's a young Greek physician and surgeon, a former classmate of the famous Hippocrates in fact, whose gambling habits have compelled him to join up with a ragtag bunch of mercenaries searching for booty up and down Asia Minor. Unfortunately the outfit had the poor sense to try to match arms with the Chadesian Amazons on the frontier of the upper Thermodon River. As one of the few mercenary survivors of the battle, he tries to patch up his compatriots and so impresses Melanippe, Battle Commander of the Chadesians, that she takes him as a prisoner of war and has him serve as her encampment's surgeon.

And from there, Xander does indeed find booty. Not as he first envisioned, but specifically that of Melanippe but most especially Helena, the young combat trainee who becomes the first known submissive in Amazon history.