City of famous mausoleum containing old Greek meeting-place (5)
I believe the answer is:
agora
'greek meeting-place' is the definition.
(public space in ancient Greece)
'city of famous mausoleum containing old' is the wordplay.
'city of famous mausoleum' becomes 'Agra' (the Taj Mahal is in Agra).
'containing' indicates putting letters inside.
'old' becomes 'o' (common abbreviation eg in OE for Old English).
'agra' going around 'o' is 'AGORA'.
(Other definitions for agora that I've seen before include "Meeting-place in Athens" , "(Many-headed) monster" , "Ancient Greek marketplace or assembly area" , "11 [LOLLY] to Ben-Gurion" , "One hundredth of a shekel" .)