"Can be deployed in combat just like any troop, but does not move. Fire stones that hit an area and has a very long range (longer than Archer's Tower). This attacks primarily towers and does not loot."
Siege Tower is the first tower that can be used offensively. You can deploy this tower in a battle, just like you would like when you are building a normal tower. This tower does massive AoE damage. The Siege Tower favorite target are defensive towers, when there are no more defensive towers in range it will attack the next closest object, including walls. Siege Tower can be produced in the Blacksmith
The Siege Tower is an Event Item which can only be unlocked at the Event Store. You will need to gain Event Points in the Event to be able to unlock the Event Items.
The Siege Tower originally didn't loot, but now it does loot even though this change hasn't been mentioned anywhere on the official pages or forum. It now has a 1x multiplier on hit for loot, which basically means it loots the damage it does (3300). Normal mercenaries have a 0,45x on hit for loot.