Friend comes to Rome rebuilt as capital (7)
I believe the answer is:
palermo
'capital' is the definition.
(I've seen this before)
'friend comes to rome rebuilt' is the wordplay.
'friend' becomes 'pal' (pal can mean a friend).
'comes to' means one lot of letters go next to another.
'rebuilt' indicates anagramming the letters.
'rome' is an anagram of 'ermo'.
'pal'+'ermo'='PALERMO'
'as' is the link.
(Other definitions for palermo that I've seen before include "ity of Italy" , "Capital city of Sicily" , "Italian city" , "Main city of Sicily" , "Sicilian port" .)