hmm, let me say something from my experience with such an occurance. I usually don't tell my Hoplites/Pikes to use the phalanx until I get within range of the enemy, in an area where I know I can use it effectively, also try and support them with other units like cavalry, peltasts or archers. oh yes and onagers definately, I usually use them to make a huge gaping hole in the enemy's wall, then pour through it. and I mean maybe even a whole section of wall, I usually use all my onager's ammo to hit the walls and then charge in. sorry if this has been said already