Man in stronghold ... (6)
I believe the answer is:
castle
I believe this is a double definition.
'man' is the first definition.
('man' can mean a chess piece)
'stronghold' is the second definition.
(I know that castle is a type of citadel)
'in' acts as a link.
(Other definitions for castle that I've seen before include "man of 1d [ADVENTURE]" , "Left's Social Services secretary" , "ancient building?" , "a piece in the corner" , "Citadel" .)