You Will Have 2 Hasati one veltes and 1 General What I do is normally make the veltes come up on the left side and fire o the rebel Militia while I position my cavalry behind them (I also bring One Hasati on the middle and one on the right side so completely blocking off all escape) so when My veltes have run out of spears to throw and I start my full assault it will be a unison strike from my Hasati and Cavalry on the Peasants and Pikemen There morale already weakened from the veltes throwing spears they will be a either more easy match for your men or they will route and if that happens you will be given the screen with 2 options saying Continue battle or end battle (I never end it because its fun watching them get owned with this strategy ) If you end it you will see there was VERY little loses from the veltes. Move 2 generals with 1 unit of Hasati each by the river (NOT merged separated) one by the bridge and 1 a little further away and up the river thus giving you a strategic point when a enemy gets into your heartland.
I normally put in the commission once this is done for another 3 Hasati I know its a lot but It will be a garrison for Segasta and the other cites while your main army is attacking Patavium and the other Gallic village.