society > armed hostility > defence > defensive work(s) > earthwork or rampart > [noun] > side of ditch nearest to parapet (6)
Fortification = escarp, n. 1.
‘A steep bank or wall immediately in front of and below the rampart‥generally the inner side of the ditch’ (Adm. Smyth).
Ground cut into the form of an escarp for the purpose of fortification.