The most common and most likely answer to this crossword clue is the 7 letter word KREMLIN
K
R
E
M
L
I
N
More clues leading to the result KREMLIN
- Where was crackpot like Mr Stalin in the end?
- Kraftwerk, REM, Lindisfarne touring Russian venue
- Where to find a crackpot like Mr Putin, ultimately?
- Nothing leads this writer, discontented refusnik, to back foreign government
- King goblin lacking leader for fortress
- Merlin wanders round behind king in citadel
- King repositioned Merlin to seat of government
- Russian establishment‘s source of trouble after change of leader
- Troubled Merlin follows king into citadel
- King has troublemaker beheaded in Russian fortress
Buddy explains!

The straight part
We know that "Russian citadel" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case russian citadel = kremlin.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does KREMLIN mean?
KREMLIN noun- (Russian architecture) A fortified, central complex found in various Russian cities.