War in ancient times was brutal. Men would battle against men, fighting tooth and nail to survive. After a war, the males on the losing side would most likely meet their end, while the females would be taken and sold as slaves.
You are an aberration: A female who takes up arms and fights alongside the men. Skilled with both sword and bow, you feel you are a match for any man. Indeed, many men have challenged you, and you defeated them. Amongst your people you are somewhat of a legend. Some call you an amazon, other seeing your great beauty describe you as a valkyria.
But now, your country is engaged in a war, and despite your best efforts, your side is losing. Having been made captain over a hundred men, you prepare them for a last stand. A glorious charge into the blackness of death, and the rewards that await you in the afterlife.
However, you aren't rewarded with death. Instead you suffer the indignity of being captured. The enemy takes you prisoner, and now they must decide what to do: do they treat you like a man and kill you, or do they see you as a woman, and take you slave? Do they recognize your power, your potential for resistance? Perhaps they use you as a trophy to humiliate and torture, emphasizing their country's victory over yours.
Please PM me if you're interested in this concept. It could go in many possible directions, but will almost certainly contain plenty of nasty cruelty. Of course, it won't just be a montage of pain and humiliation -- there will be plenty of scope for you to try to fight or escape. Get back at your captors. Meet other slaves and see if they can provide you with anything to help you escape.
Let me know of any limits or inhibitions you might have before we start! :)