The most effective siege unit, has a 5% chance per level to make hole in the wall. If failed there is 2% chance to destroy one level of a wall. If there is no wall, then target the castle. If that does not exist either, damage a random building. If that fails, then they have a 1% chance per level to damage a random building.

Needed to train
Iron 50
Wood 150
Stone 100
Gold 3500
Duration 4.2 h
The unit's info Level 1 Level 5
Attack 1 5
Defense 0 0
Movement 2 2
Max level 5 5
Residents 50 50
Stone -24 /h -24 /h

Note: do not use trebuchets if you want to conquer city you are attacking theu can deal huge damage to buildings