Priam's city (4)
I believe the answer is:
'priam's city' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for troy that I've seen before include "Ancient city associated with a wooden horse" , "System of weights introduced by French" , "Weight system - old city" , "Where beautiful Helen came from" , "City besieged to releae Helen" .)