bulwark

(noun) an embankment built around a space for defensive purposes. Synonyms: rampart, wall. Examples: "They stormed the ramparts of the city." "They blew the trumpet and the walls came tumbling down."

(noun) a fencelike structure around a deck (usually plural).

(noun) a protective structure of stone or concrete; extends from shore into the water to prevent a beach from washing away. Synonyms: breakwater, groin, groyne, mole, seawall, jetty.

(verb) defend with a bulwark.