I'm assuming almost none of it is based on history really (other than the invasion). It all felt a bit far-fetched and the main character being a slave who is somehow the best swordsman in the land was quite ridiculous. The Three-way duel at the end felt a bit over the top with the slow-mo too, like it was directed by Zack Snyder. In fact I can see a comparison to 300, very stylish but a little lightweight.