Yup and history in general works well. Authentic history and embellished history tends to be a very exciting "fantasy" world.

Heck, look at the Total War games:

Shogun: Total War

Medieval: Total War

Rome: Total War

Medieval II: Total War

Empire: Total War

Napoleon: Total War

That is great, and I am personally a great fan of Celts.

However, what's up with the elves, trolls, orcs...? These are well-understood races, are they free to use?

I agree. Age of Mythology, for instance, is a great game which combines Greek, Egyptian, and Norse mythology as three separate groups and stages into one story.