Well, hmmm. Modern stereotypes (allowing for variation between cultures) that have their roots in classical and medieval Christian thought, such as the beliefs that women make decisions in emotion (and that this is bad), or that women should be sexually restrained and chaste, for example. I've read Celtic-era fiction where people expressed those kinds of opinions and--well, the male heroes of Celtic myth make hot-headed decisions all the time, and the women blithely sleep around without censure (and even allowing for exaggeration on the part of the Romans, the latter is backed up with earlier historical sources). So then I find myself thinking "why do these Celts sound like medieval Englishmen/modern misogynist jerks?" and I'm thrown out of the story.