rampart

Short definition from Wiktionary

Noun

1. 1
   A defensive mound of earth or a wall with a broad top and usually a stone parapet; a wall-like ridge of earth, stones or debris; an embankment for defensive purpose.
2. 2
   A defensive structure; a protective barrier; a bulwark.
3. 3
   That which defends against intrusion from outside; a protection.
4. 4
   A steep bank of a river or gorge.

Verb

1. 1
   To defend with a rampart; fortify or surround with a rampart.