Most historical fiction uses anachronism (noble exception is Patrick O’Brian), especially the use of modern jargon (Tom Holt’s hilarious books on Ancient Greece are a good example.) Last night I was reading an excellent novel set in Ancient Rome. The author uses lots of modern jargon “he’s nuts; stop faffing about” which I could deal with. But then the author used doolalli to describe someone who was insane. This term comes from the Deolali Barracks in India where nineteenth century British soldiers with mental problems were sent. Where do you draw the line?