How to win the battle of Carrhae in Rome: Total War

In a nutshell: send the Roman Cavalry after the horse archers in the back of your army. Have your men unform the testudo and make two battle lines, one behind the other. Send your bodyguard after a unit of horse archers. When the Cataphracts charge the front line, have your second line attack, and make the general attack from behind. Try to kill enemy generals. After all that, have fun moping up the horse archers (nah, it's not that fun. you have to use a bunch of slow heavy cavalry or infantry to force them to rout)!