Plates one purchased in Greek city (6)
I believe the answer is:
delphi
'city' is the definition.
(I know that Delphi is a ancient city)
'plates one' is the wordplay.
'plates' becomes 'delph' (I can't justify this - if you can you should believe this answer much more).
'one' becomes 'i' (Roman numeral).
'delph'+'i'='DELPHI'
'purchased in greek' is the link.
I am not very happy about this link. Some or all of it may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for delphi that I've seen before include "Scene of Greek oracle" , "Place of the famous oracle" , "'In Greek mythology, the site of the oracle (6)'" , "Ancient Greek sanctuary dedicated to Apollo" , "Old Greek city" .)