For over 4000 years, the world's greatest empires have come and gone. Only one has survived the test of time: China. Century after century, China's regal emperors mobilized immense peasant armies to accomplish engineering feats unparalleled in human history. Among the groundbreaking innovations of the ancient Chinese were the world's longest canal, its most complex and effective irrigation system, and a naval fleet mightier than all those of Europe combined-but, none can compare to the colossal 4,000-mile wall that stands as the most ambitious construction project ever built. From such heights came spectacular death spirals, as dynasty after dynasty-consumed by vanity and greed-was stripped of power by the people it had ruled.