A strong defensive wall or barrier protecting a place, or anything that serves as strong protection against something dangerous.
From Dutch 'bolwerk' (literally 'round-work'), combining 'bol' meaning round and 'werk' meaning work, originally referring to rounded bastions in medieval fortifications.
Bulwarks were designed to be rounded instead of angular because cannonballs would bounce off curves instead of smashing through sharp corners—this practical physics lesson is literally built into the word.
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