Artillery only buildable as siege equipment?

[scouserlee]

Is making onagers, ballistas and scorpions of all types only buildable during sieges a realistic proposal within the game engine limitations? I'm a total noob at modding, I'm assuming this would this be experienced modder only territory?

[valerius karamanus]

It may be possible but ballista-scorpion etc are classified as units and they require a crew to be operated afaik. So even if we can spawn ballistas in siege battle, player would still need to have crew peasants in order to use them. This would bring interesting campaign recruitment changes nonetheless. I like the idea.