Thats what garrisons were for in medieval times.
trebuchets have little iron thingy that you can move up and down for the range of fire (dont know how to say better)
i did this aswell and did a post about that on reddit
It doesn't necessarily need to be raided, but simply the market gets out bought, because other cities in the area have a food shortage, even enemy cities and neutral caravans buying out your town because their town has higher prices. So you have now a shortage in food aswell and your garrison dies because of this.
Yeah you're right haha but still they always have different weapons. So yeah 50/50 chance