I am using Onagers or/and archers with flaming ammo to kill and legionaires to stop them. Usually I place my army in a half circle around a hill with deep legionary formations as front rank and everything else behind them. It is difficult for the Ai to outflank me and for the chariots to charge uphill. Most chariot units are routing after they can`t break the legionary line and after receiving high casualties by the missile troops before . Especially the onagers have a high range and can kill several chariots with one hit.