Bulwarks (8)
I believe the answer is:
ramparts
'bulwarks' is the definition.
('rampart' can be a synonym of 'bulwark')
This is all the clue.
(Other definitions for ramparts that I've seen before include "Fortified earth banks topped with parapets" , "Defensive walls with parapets" , "used defensively" , "Earth banks as fortifications topped with parapets" , "Defensive walling" .)