Ok, thanks. So there's a difference from Medieval then?

Because as far as I can remember in Medieval it was something like:

Easy: Player gets morale bonus and the AI uses dumbed-down tactics.
Normal: Normal AI tactics and no bonuses to anyone.
Hard: Better AI tactics, still no bonuses to anyone.
Expert: Beefed up AI as well as a morale bonus to it.

From what I hear here the AI in Rome gets various bonuses even on hard.
I don't like cheating AI, let it use the best tactics it can but don't let their peasants be stronger than mine... :P