After ceremony, regularly revisit ancient city (7)
I believe the answer is:
pompeii
'ancient city' is the definition.
(ancient Roman city)
'after ceremony regularly revisit' is the wordplay.
'after' is a charade indicator (letters next to each other).
'ceremony' becomes 'pomp' (I've seen this in another clue).
'regularly' means one should take alternating letters (regularly take one letter, leave next etc.).
The alternate letters of 'revisit' are 'eii'.
'pomp' next to 'eii' is 'POMPEII'.
(Other definitions for pompeii that I've seen before include "Former city" , "town coming to a terrible end" , "Ancient site" , "Ancient Italian city" , "Italian town near Naples buried by Vesuvius in AD 79" .)