Announcement about Roman capitol (12)
I believe the answer is:
proclamation
'announcement' is the definition.
(I know that announcement can be written as proclamation)
'about roman capitol' is the wordplay.
'about' indicates an anagram.
'roman'+'capitol'='romancapitol'
'romancapitol' is an anagram of 'PROCLAMATION'.
(Other definitions for proclamation that I've seen before include "Official announcement" , "Public announcement" , "Official public declaration" .)