Defensive structure (13)
There are a few possibilities for this:
fortification
'defensive structure' is the definition.
(I know that rampart is a type of fortification)
This is the entire clue.
(Other definitions for rampart that I've seen before include "Castle embankment" , "section of defence?" , "Broad defensive wall" , "Battlement, fortification" , "Defensive structure" .)
'defensive structure' is the definition.
(I know that redoubt is a type of fortification)
This is the entire clue.
(Other definitions for redoubt that I've seen before include "Entrenched stronghold" , "Temporary military fortification" , "Defensive outwork" , "Obtrude in kind of military fieldwork" , "Military defence-work" .)
'defensive structure' is the definition.
(fortification is a kind of defensive structure)
This is all the clue.
(Other definitions for fortification that I've seen before include "Eg, a defensive wall" , "Strengthening" .)