From Middle Dutch 'bolwerc' (plank-work)—also the source of French 'boulevard,' built where ramparts once stood.
A solid wall-like structure built for defense; also, a ship's side above the upper deck.
From Middle Dutch 'bolwerc' or Middle High German 'bolwerc,' from 'bol' (tree trunk, plank) + 'werc' (work, construction). A bulwark is literally 'plank-work'—a wall built from heavy timbers. The nautical sense came from wooden reinforcements along a ship's gunwales. Key roots: bol (Middle Dutch: "tree trunk, heavy plank"), werc (Middle Dutch: "work, construction").