Way to capture foreign part of fortification (7)
I believe the answer is:
salient
'part of fortification' is the definition.
(historical part of a fortified building)
'way to capture foreign' is the wordplay.
'way' becomes 'st'.
'to capture' means one lot of letters goes inside another.
'foreign' becomes 'alien' ('alien' can be a synonym of 'foreign').
'st' enclosing 'alien' is 'SALIENT'.
(Other definitions for salient that I've seen before include "Conspicuous; pointing outwards" , "obvious" , "Outstanding - it's lean (anag)" , "Prominent, most noticeable" , "Foremost" .)