I agree with you Winston that cities surrounded and under seige for prolonged periods of time would collapse with regard to their INDUSTRY and their ability to provide an increase to the defense of its garrison, but there would have to be variants. The larger the city, the longer it survives. Also, take into consideration the scenario of Leningrad during WW2. There was air supply and sea supply, and although both very limited, the citizens managed to hold out for over a year.
Yeah, I agree - I was only sketching out the idea at the time as I didn't want to get into too much detail. My thinking on seiges would be this:
Need to surround a city by placing a land unit in all adjacent land tiles to start a seige.
Towns/Cities/Metropolises can all hold out for 2 turns minimum but things such as city walls, granaries, hospitals, airports, civil defense, rivers/fresh water lakes, aquaducts & palaces all lengthen the amount of time that a settlement can hold out - airports would add alot of turns (say 4 or 5 maybe), the others would only add 1 or 2 turns. Once the turns are up, that settlement is starved into submission and surrenders.
Whilst under seige, a settlement cannot work any tiles apart from the central city tile and it also doesnt benefit from any strategic resources/ luxuries. Chances of plague/disease massively increase.
Coastal settlements are immune to seige unless a naval blockade is also in place.
Impassable terrain (such as fresh water lakes) doesnt count when surrounding cities.
This would add to strategy by forcing civs to sally out and engage attackers as opposed to simply sitting 20+ spearmen in a fortified capital on a hill - as so often happens when I'm attacking another Civ.