Hasten rebuilding of capital (6)
I believe the answer is:
athens
'capital' is the definition.
(capital of Greece)
'hasten rebuilding' is the wordplay.
'rebuilding' is an anagram indicator.
'hasten' with letters rearranged gives 'ATHENS'.
'of' is the link.
(Other definitions for athens that I've seen before include "City of the Parthenon" , "Hasten (anag) -- capital city" , "Tan she got in Greece" , "Hen sat down in the city" , "foreign city" .)