Miniature version of ancient city, omitting river (3)
I believe the answer is:
toy
'miniature version' is the definition.
'ancient city omitting river' is the wordplay.
'ancient city' becomes 'troy' (I've seen this before).
'omitting' is a deletion indicator.
'river' becomes 'r'.
'troy' with 'r' taken away is 'TOY'.
'of' is the link.
(Other definitions for toy that I've seen before include "Doll or teddy, say" , "Trifle or dally with" , "One of spelt out words" , "A child's plaything" , "Child's amusement" .)