Platforms in section of ramparts originally set up (6)
I believe the answer is:
rostra
'platforms' is the definition.
(rostrum is a kind of platform)
'section of ramparts originally set up' is the wordplay.
'section of' indicates a hidden word.
'set up' is a reversal indicator.
'artsor' is hidden in the letters of 'ramparts originally'.
'artsor' back-to-front is 'ROSTRA'.
'in' is the link.
(Other definitions for rostra that I've seen before include "Raised platforms" , "The beaks" , "where they make their speeches?" , "stages" .)