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（尤指古代的）土木防御工事，土垒
Earthworks are large structures of earth that have been built for defence, especially ones which were built a very long time ago.
例句
Europe's biggest Stone Age earthworks are at Silbury Hill in Wiltshire.
欧洲石器时期最大的土木防御工事位于威尔特郡的西尔布利山。