rampart

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.

A defensive structure; a protective barrier; a bulwark.

That which defends against intrusion from outside; a protection.

(usually in the plural) A steep bank of a river or gorge.

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