I only mostly use them for sieges; when I have money that is, and typically only for the duration of a war. I tend to have two stacks on campaign in that event: a full "fieldstack", with the main units, and a siege train stack, with a couple of different types of catapults, of course guarded by a detachment of cavalry.
beyond sieges, I never found that much use for them-except in moments of desperation, such as against elephants or something. for them to truly be useful, I'd ideally need them to be more mobile, able to go along with even cavalry. maybe a small catapult on a cart or something![]()
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