City fortress (7)
I believe the answer is:
citadel
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">city fortress</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for citadel that I've seen before include "secure place" , "Urban fortress" , "Keep - castle" , "Urban stronghold - dialect (anag)" , "where Salvationists meet" .)