The Tower of London was primarily a fortress protecting the city of London. It was also used by the Kings & Queens of England as a royal palace and as a prison.
Alhanbra
citadel- a fortress in a city.
If it is in a city, acropolis(high city).
Polis is the Greek word for a city-state, that is a tract of farmland on which was built a city and its protective fortress (acro-polis = high city, that is the fortress on a hill, around which the city came to be built). It was independent - self ruled - which is why the term city-state is used.
crusaders
he is at the pewter city museum
A zwinger is a citadel or fortress, especially one which protects a city.
Dickville suckers
It means 'high city' - it was originally the fortress of the city and then had temples erected on it when the city itself became walled.
Sevastopol
An acropolis, acro = highest, polis = city, the citadel of a city which formed the basis and refuge of its defence against invaders.