I find it almost impossible to take cities guarded by massive amount of archers and have stone walls and higher. They pretty much drive back any attack by shooting my men to death or shooting their seige engines to death. I do have some onagers but they simply dont have enough ammo. 3 groups can barely take out two wall section and this doesnt help me at all.

The only thing I can think of is to make a full stack of onagers and completely level the city. However that's pretty hard and the onagers are pretty slow moving as well and I am far away from my heartland. I am not Egyptians so I cant form the turtle and wait for enemy archers to run out of ammo. Desert axemen will rout as soon as they get in the hole in the wall from the hail of arrow.

please help