Duplicate Mediterranean city corporation (5,4)

I believe the answer is:

spare tyre

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'corporation' is the definition.
(I've seen this before)

'duplicate mediterranean city' is the wordplay.
'duplicate' becomes 'spare' (I can't explain this - if you can you should give a lot more credence to this answer).
'mediterranean city' becomes 'tyre' (I've seen this before).
'spare'+'tyre'='SPARE TYRE'

Can you help me to learn more?

(Other definitions for spare tyre that I've seen before include "Roll of fat around the tummy" , "Middle-age spread" , "evidence of overindulgence" , "Extra fat around the waist" , "good for a flat exchange?" .)

I've seen this clue in The Guardian.

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