Senlis on 10 August 2009
Age of Empires 2 is really good. It is medieval themed, and resembles Command and Conquer games in gameplay.
Medieval 2: Total War is my other recommendation. it is more strategically sound than AOE and therefore makes you think more. Also is more historically accurate in it's gameplay. Also a lot more fun than AOE or any other strategy game I can think of from that era.
That being said, my highest recommendation for an RTS is World In Conflict, but that is 20th century based, so that does not match your requirement.
