Plural of breastwork; multiple low defensive walls or fortifications constructed for military protection.
Simply the plural form of 'breastwork' (breast + work). The term became standard in military terminology by the 17th century during the age of European fortifications.
The American Civil War made breastworks famous again—soldiers would spend nights building earthen breastworks before dawn battles, and many Civil War battlefields still show the curved lines of these quick defenses!
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