Ancient city not wholly in South Africa (6)
I believe the answer is:
sparta
'ancient city' is the definition.
(I know that Sparta is ancient)
'not wholly in south africa' is the wordplay.
'not wholly' becomes 'part' ('part' is the opposite to 'wholly').
'in' is an insertion indicator.
'south africa' becomes 'SA' (abbreviation).
'part' going into 'sa' is 'SPARTA'.
(Other definitions for sparta that I've seen before include "Ancient country" , "place of austerity" , "Ancient Greek city-state" , "found in Ancient Greek location" , "in ancient Greece" .)