Prince entering capital city of ancient Greece (6)
I believe the answer is:
delphi
'city of ancient greece' is the definition.
'delphi' can be an answer for 'city' (Delphi is an example). I'm not certain of the 'of ancient greece' bit.
'prince entering capital' is the wordplay.
'prince' becomes 'p'.
'entering' means one lot of letters goes inside another.
'capital' becomes 'delhi' (I've seen this before).
'p' placed into 'delhi' is 'DELPHI'.
Can you help me to learn more?
(Other definitions for delphi that I've seen before include "Where god used to speak" , "Greek site of Apollo's most famous oracle" , "Place of Greek oracle" , "Sacred site" , "Dead ringer" .)