I'm new to the game, so I was playing as Jullii on "easy." I had captured Thapsus, and had a garrison of mostly hesati, and archers. A Carthagian Army(2000 strong) camped outside my city. I attacked them before they attacked me.

I sent all my archers onto the walls, and killed every single man on the battlefield, except the general and his bodyguard. When he started galloping away, I sent about 200 horsemen after him. He got away though. I only sustained six deaths, who were accidently shot in the back.