Assertion: castle's defence | /r/HasProperty | supported by a line of four earthwork forts
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text: These defences, known as the castles of the Downs, were supported by a line of four earthwork forts, known as the Great Turf Bulwark, the Little Turf Bulwark, the Great White Bulwark of Clay and the Walmer Bulwark, and a 2.5-mile (4.0 km) long defensive ditch and bank.