Crossword Clue:

a fortification of earth

Answer	Crossword Clue
BASTION	Part of a fortification.
SIEGE	Encirclement of a fortification.
CAPONIERE	In fortification, part of a ravelin

ESCARP	Steep slope in front of a fortification
MOAT	Trench around a fortification
REVET	Build a retaining wall, as a fortification.