"You cannot demolish castles, ports and roads, or speciality buildings at their base level." - In game message.
WHAT??? Why can't we at least downgrade castles to their base level? This makes no sense to me considering most AI cities that you conquer have relatively high castle upgrades. Since they are so tied to rice, which can cause huge issues for an empire, why couldn't you downgrade them?
Is this a bug or "feature"? Anyone know the rationale for it if it is a feature?
edit - That in-game message is sort of confusing, especially since you can demolish upgraded ports.