What source of stupid things that AI may do when their city is under sieged?
A. They may start building a Wonder. If they do this, move your all your Quechua away from their city for about 2 or 3 turns.
B. They may start building settler. I like this part...free worker and experience.

Just anticipate where they they may send their settler out next and ambush them out in the open field.
C. They set out to destroy our cities. I love this part...when the AI put their minds into something, they won't be sidetracked...if their mission is to destroy our city or pillage our land, nothing else matter. We just wait to engage them in the open meadow in between our city and their.