Old city that's almost perfect (6)

I believe the answer is:

thebes

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'old city' is the definition.
(ancient Greek city)

I don't understand the rest of the clue.

(Other definitions for thebes that I've seen before include "Ancient Egyptian or Greek city" , "Ancient Nile city" , "Greek city of Oedipus" , "place in Greece" , "Old city of Greece or Egypt" .)

I've seen this clue in The Guardian.

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