Russian citadel (7)
I believe the answer is:
kremlin
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">russian citadel</span>' is the definition.<br/ ><span class="explanation-format__explanation">(building in Moscow)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for kremlin that I've seen before include "House of the Russian government" , "Symbol of the Russian government" , "Seat of Russia's government" , "fortress" , "Citadel of a Russian town" .)