Lasting conclusion about old city (8)
I believe the answer is:
enduring
'lasting' is the definition.
('endure' can be a synonym of 'last')
'conclusion about old city' is the wordplay.
'conclusion' becomes 'ending' (synonyms).
'about' means one lot of letters goes inside another.
'old city' becomes 'ur' (ancient city state).
'ending' enclosing 'ur' is 'ENDURING'.
(Other definitions for enduring that I've seen before include "stable ..." , "Putting up with patiently" , "Putting up with something" , "having lasting qualities" , "Bearing patiently or lasting" .)