I have a huge problem with completing this mission. You have to banish 10 pirates into the crater. I have already done this with 7 of them but... the remaining 3 pirates are in the tower. I can't destroy the tower because the balista won't get through the mountain passage. How do I get them out of this tower? If I simply attack them with my soldiers they get killed and I lose. I am helpless :(

EDIT: Problem solved. The catapult DOES go through the passage, but in my case it was blocked by a pile of fish that I created when testing different spells.