i need some advice assaulting stone walls. whenever i am forced to siege a city with stone walls, i usually sustain heavy casualties. units scaling the walls with ladders get wiped out almost immediately. siege towers usually get burned or even if they do get to the wall, the units get wiped out since i can't get other units to support them.

now i usually still win the siege by distracting one part of the defense while a unit sneaks onto an undefended part of the wall, and then moving to the nearest unguarded gatehouse, thus allowing the rest of my army to occupy the square, but i have to sacrifice many units to do this, usually up to half of my standing army if i'm facing a well defended city.

so my question is what kind of unit should i send to the walls with high survivability rates? how can i prevent the assaulting units from being isolated and surrounded on the walls from all sides? or simply put, how can i minimize my casualties when assaulting stone walls, other than just starving out the city?

i am playing as hayasdan by the way. the units i use to assault the walls are usually medium armenian infantry and persian hoplites. they get slaughtered by seleucid or ptolemaioi native or medium phalanxes on the walls.