 The film features catapults resembling windmills , that can fire rapidly , and a ballista that can fire three projectiles at a time . The practical versions of these were metal with fibreglass painted and aged to resemble wood on top . Weta created props of the missiles thrown by the Telmarine equipment . The practical version of the catapult had its upper half painted blue , to composite a digital version programmed for rapid firing movement . 
