What is a Catapult unit?
Catapults can destroy your opponent's buildings. If you initiate an attack with catapults, you can select which building is targeted in the window from which you launch the attack. Using the "catapult target building level" in the simulator, you can simulate how many catapults you will need to partially or completely destroy a building at level X. It doesn't matter which building you're attacking; only the level is decisive, with the exception of the church. This means that in order to destroy an academy at level 1, you need just as many catapults as you do to destroy a smithy at level 1.
The following buildings can not be demolished below level 1: Village headquarters, Farm, Warehouse.
The hiding place cannot be attacked with Catapults.