A line of fortifications or defensive walls built completely around a place to surround and isolate it.
From Latin circumvallatio, noun form of circumvallare. The term became standard in military science and engineering during the Renaissance when siege warfare tactics were systematically studied and documented.
Archaeologists have found circumvallations that are over 2,000 years old, preserved as crop marks visible from aircraft—the soil compacts differently over ancient walls, creating ghost outlines you can only see from above.
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