Small, ancient city, authentic and bizarre (7)
I believe the answer is:
surreal
'bizarre' is the definition.
(I've seen this before)
'small ancient city authentic' is the wordplay.
'small' becomes 's' (abbreviation - e.g. clothes size).
'ancient city' becomes 'ur' (ancient Sumerian city state).
'authentic' becomes 'real' (I've seen this before).
's'+'ur'+'real'='SURREAL'
'and' acts as a link.
(Other definitions for surreal that I've seen before include "Dreamlike - Dali-like" , "Not of this world" , "Dali being so?" , "Bizarre, fantastic" , "Weird; dreamlike" .)