The Acropolis, for example (7)
I believe the answer is:
citadel
'the acropolis for example' is the definition.
(acropolis is a kind of citadel)
This is all the clue.
(Other definitions for citadel that I've seen before include "secure place" , "Urban stronghold - dialect (anag)" , "place of refuge" , "Fortress overlooking a city" , "Fortress (in or near city)" .)