Bulwark is a noun that has its sources in Middle English and Middle Dutch from the 15th century. In Middle English it comes from the word "bulwerke." In Middle Dutch it comes from the word "bolwerk." The components of the Dutch origin are "bolle" (tree trunk) and "werc" (work).
Bulwark is also an architectural term for a wall that supports other parts of a structure.
Bulwarks are also called fortresses and ramparts. They were used during the Middle Ages as a part of a castle's defense.
Bulwarks also refer to the side of the ship that lies above the upper decks.
Finally, bulwark is sometimes used as a metaphor in speech and literature. A concept or idea is often said to be a bulwark against a unpleasant outcome. For example, in American political rhetoric, America was presented as the last bulwark against a communist takeover during the Cold War.