Like the other dedicated siege weapons, towers aren't built from any building and do not exist as an individual unit. They are instead constructed by the attacking army directly on the battlefield after having laid siege to an enemy settlement. Building a Siege Tower costs 100 build points.
When the attacking army assaults the settlement, any tower in the army is assigned to an infantry unit that will push it towards a section of the enemy wall. Pushing a tower substantially reduces a unit's speed and prevents it from running, though the tower also provides some cover against enemy missile fire.
When a Siege Tower reaches the fortification, it will drop a gangplank between it and the wall; troops could then rush onto the walls and into the castle or city. If the pushing unit is wiped out, another can take the tower and continue pushing.
Siege Towers can catch fire and become destroyed if constantly attacked by enemy missile units. When the siege ends (for any reason), Siege Towers are abandoned.
The Gohma utilize a unique variant of the Siege Tower.