Crossdressing Women
Cross-dressing has, in romantic fiction, always been an option for women to go off to war. A woman who can pass as a man has all of the social obstacles to her martial career removed for as long as she can pull it off. Of course, to pass as a man, she had better be pretty ugly (or she will forever be someone’s squire), and have an explanation for her lack of a beard (easier to do in Christendom than pagan Scandinavia). If she is caught, she is in deep trouble — remember, the execution of Joan of Arc isn't for heresy, it is for transvestism.