Instead of discarding certain cards, like fortresses and sites; why not leave them in play face down with no abilities. I know this isn't exciting or anything, but the following scripture is an example of a command to utterly destroy a city (Israelite) if it got caught up in idolatry. The remains, v. 16 calls it heap, were to stay around as an example to future Israelites. The NIV translated heap into ruin. Its more for scripture accuracy.
Deuteronomy 13:12-16 (King James Version)
12If thou shalt hear say in one of thy cities, which the LORD thy God hath given thee to dwell there, saying,
13Certain men, the children of Belial, are gone out from among you, and have withdrawn the inhabitants of their city, saying, Let us go and serve other gods, which ye have not known;
14Then shalt thou enquire, and make search, and ask diligently; and, behold, if it be truth, and the thing certain, that such abomination is wrought among you;
15Thou shalt surely smite the inhabitants of that city with the edge of the sword, destroying it utterly, and all that is therein, and the cattle thereof, with the edge of the sword.
16And thou shalt gather all the spoil of it into the midst of the street thereof, and shalt burn with fire the city, and all the spoil thereof every whit, for the LORD thy God: and it shall be an heap forever; it shall not be built again.
