As I recall from a thread, walls doesnt do anything for public order.

And flaming arrows, should be more effective against elephants and cavalry I seem to have read elsewhere. Plus, whenever I got elephants (Seleucids, carthage, parthia) and the enemy has archers, the enemy AI uses flaming arrows against my elephants.

And onagers with flaming ammo is awesome against big blocks of infantry...as long as they got some experience.