I was visiting a village Verkhnyaya Balcariya (Upper Balcariya) in Cabardino-Balcariya republic (South of Russia). There I was shown the smallest fortress in the Caucasus mountains built without a base. Well, actually the building has the base, but it is a natural rock.
Such fortresses were built by the rich people of local tribes in XVII-XVIII centuries in order to hide their family members and/or valuables during the wars or the periods of blood revenge. The fortress on the picture was built in XVIII century by the Amirkhanovs family and is unique in the Caucasus as it has a rock base. Also it is very small, I can’t imagine, how people could hide in such a building and especially how to provide food and water there.
The only thing I can really prove - it is very difficult to get in, if you don’t have a ladder or you are not an alpinist. I tried several times but failed.