I was experimenting with the Gaul Swordsmen's war cry. Finally turned on tactical advice and it said to use the war cry shortly before charging. Your guys will shout, then bang on their shields. It really seemed to help their charge. Don't know if it adds morale or bonuses at any other time (I think not from messing with it before in other situations.) They tore up the Principes they first encountered on the charge--kill speed was fast. Looks like a "turbo" charge setting.