Though slow in movement, Siege Towers have the ability to move straight up to an enemy wall, lower the platform and allow vast amounts of troops up onto the enemy walls in a short space of time. Note that Siege Towers can only do this on walls, and not on Gatehouses or Towers.
Siege Towers react well to missile fire by ranged units, and can sustain a fair amount of damage. However, melee troops on the ground can quickly overwhelm it if they can get close enough. Good protection is therefore required when utilising this unit.
Once a Siege Tower has lowered its platform in this way against a section of wall, it remains immobile throughout the entire duration of the game and to remove it, the unit must be disbanded.
There are two distinct types of Siege Towers in Stronghold 2. Neither have any remarkable differences as both do the same thing, although the larger Siege Tower moves slower due to its size. Larger Siege Towers also have more durability than their smaller counterparts.
You can recruit a Small Siege Tower from the rank of Knight Errant, and a large Siege Tower from the rank of Royal Champion. You will need 150 gold for a Small Siege Tower and 250 gold for a Large Siege Tower, along with 4 peasants from the campfire before you can recruit either Siege Tower.