Former empire ship found in ancient city (4)
I believe the answer is:
ussr
'former empire' is the definition.
(I've seen this in another clue)
'ship found in ancient city' is the wordplay.
'ship' becomes 'SS' (prefix in ship names eg SS Great Britain).
'found in' means one lot of letters goes inside another.
'ancient city' becomes 'ur' (ancient Sumerian city state).
'ss' placed into 'ur' is 'USSR'.
(Other definitions for ussr that I've seen before include "Former federation of Russial and other states" , "Former association of communist republics" , "Country established in1922 and dissolved in 1991, in short" , "Former union of socialist republics" , "Former Soviet Union" .)