Is there a way to make buildings go obsolete after your research has reached a specific point?
I mean, the balistatower shouldn't be build after you discover cannonmaking, you should have cannon-towers instead. It looks odd with cities still having or being able to build balistatowers at 2100AD.
Same goes for many more buildings
add OBSOLETE_ADVANCE to a building, and it because useless after that advance is discovered but you will continue to pay maintaence costs (i think). You need to sell off the building then.
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