It is 207 Before Christ, whoever that may be. Our Empire stands strong against its foes and our armies are currently marching westwards, invading Africa and Hispania. To our north we have Medhlan and Noreia keeping Barbarians at bay.
In the hopes of making those cities impenetrable, I, Quaestor Quintus Burrienus Brutus of the House of Junia, have asked the cities' engineers to fit the walls with Ballistae and Scorpions. Our Roman engineers being true Romans, the finest of the finest, did as I asked in merely five years, finishing work just in time before the Barbarians laid siege to Medhlan.
I set up my troops behind the gates and on top of the walls, preparing for the upcoming siege battle, then noticed that Medhlan's siege engines were missing. Although the Barbarians stood no chance against our excellent Hastati, Rorarii, and the boiling oil pouring down on them, I'm still disappointed that I couldn't try out my new toys- I mean, weapons, against the enemy.
At first I thought the Engineers hadn't finished building the siege engines, but Medhlan's and Noreia's Governors assure me they have siege weapons at their disposal: two units of Roman Bastion Ballistae and two units of Roman Bastion Scorpions each.
How come I didn't see those when preparing for defending the city? Where were they? Do I need to have the engineers build a Workshop before they can actually mount those weapons onto the walls?
TL;DR
My city should provide siege weapons during siege defense. Why were they not available during battle? Do I need to build something in the province first?
Best Answer
http://forums.totalwar.com/showthread.php/84013-How-do-you-get-deploy-defensive-artillery/page3?s=4586ab6ec43eca9ce6bbe0860dbaa500
The last post in that page says that you only get the defensive artillery if the besieging army (AI) decides to build siege equipment, even though I'm all the way up to 25 BC as Rome and have yet to have a battle where they decide to use equipment, they use the 3-5 unit rush to the gate and use their torches.