There ARE rules, y'know

"#14. As the male author of a naval or military adventure series begins to age, instances of the hero successfully cuckolding an old fool become less frequent."

Yes, there are just too many rules for an author of historical fiction to consider. Sarah's Bookarama has neatly compiled Alan Fisk's All-Purpose Rules for Writing Historical Fiction/Writing Ripping Yarns.

Authors might also want to review Reading Matter's Rules for Classical-Set Fiction, also courtesy of Bookarama.