Since the birth of agriculture, the settled populations of China’s great floodplains were perennial targets for nomadic raiders from the Asian steppes. The first attempts to block these depredations with walls date back almost 3,000 years, with many succeeding permutations. The Ming came to power by expelling the Mongols, who had conquered China via this classical invasion route: they resolved to achieve a definitive solution to the problem. Early rebuilding or existing walls was intensified after Mongol raiders captured the Ming emperor at Tumu fortress (1449). A reinforced extension across the Ordos proved its worth when the Mongols were repulsed (1482), but the nomads adapted, raiding from the west round Zhangye. Massive earthworks ending at Jiayuguan countered this threat. Stone double line defences were added round Datong, guarded by 1,200 brick watchtowers (1569–71). But unrest increased and the Ming fell when dissident forces simply opened the gates to the Manchu (1644).
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