Hmm actually the siege tower has another use. When your men first start climbing the unused siege tower, they gather at the top until there are like 20 or 30 or them, then they will all rush at the wall together. Rather useful for gaining a foothold on the wall, unless of course the first wave gets repulsed. Which means that the single ladder is not bringing up more men than are getting killed. Which means that unless you do something your men are going to walk one by one into a meat grinder. Which mean you are in a fix. So far i have no idea how to get the silly men to repeat that nice first charge. Not to say that ladders are BETTER than siege towers, because the same thing will tend to happen if you face the same sort of unit on the wall, except in multiple places. Plus you get the added bonus of arrows raining from heaven onto you men.

P.S. "The same sort of unit" refers to a bunch of Spartan hoplites. Scary people. Skewered my silver sword silver shield principes. Finally managed to kill them by halting my assault and they walked off to aid theyre comrades in dealing with another, more successful attempt on the wall. I sent up another fresh unit to deal with the Spartans and managed to get them to fight with their swords. The first unit up the wall lost 135 men. Good thing they didnt rout.