Genghis Khan built a formidable land empire, but he never crossed the sea. Yet by the time his grandson Kublai Khan had defeated the last vestiges of the Song empire and established the Yuan dynasty in 1279, the Mongols controlled the most powerful navy in the world. How did a nomad come to conquer China and master the sea?

Kublai Khan is one of history's most fascinating characters. He brought Islamic mathematicians to his court, where they invented modern cartography and celestial measurement. He transformed the world's largest land mass into a unified, diverse and economically progressive empire, introducing paper money. And, after bitter early setbacks, he transformed China into an outward looking sea-faring empire.

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