How should we tag the following types of structures?
Obviously they are very different in purpose and structure, but many travellers may not be focussed on these details and may use one term where another is more technically accurate. For a while we have had castles and the somewhat related tags architecture and landmarks. Recently tags for citadels, city-walls, fortifications, and fortresses were also added.
It's likely not be practical to have separate tags for all of them, since travellers would likely be interested in visiting any castle-like or fort-like structure, not any of these in particular.
I asked a question on English-SE some time ago about this, and most of the answers are not of great use for our site's needs. We had a small-ish discussion on meta as well, and a prolonged chat discussion a long time ago. But the issue was never resolved satisfactorily.
Vote up or down the suggestions below and add comments as necessary.
Other options? Add your own using similar format to the answers provided.