Pearl Mosque city (4)
I believe the answer is:
agra
'pearl mosque city' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for agra that I've seen before include "Site of the Taj Mahal" , "vicinity of mausoleum" , "mausoleum site" , "City in India" , "Subcontinental city" .)