Prize pub in ancient city (6)
I believe the answer is:
trophy
'prize' is the definition.
('trophy' can be a synonym of 'prize')
'pub in ancient city' is the wordplay.
'pub' becomes 'ph' (public house).
'in' means one lot of letters goes inside another.
'ancient city' becomes 'troy' (I've seen this before).
'ph' going inside 'troy' is 'TROPHY'.
(Other definitions for trophy that I've seen before include "Award for victory" , "Cup given as prize for victory" , "Prize symbolising victory" , "Memorial of victory" , "Award cup" .)