For thousands of years, fierce Mongol warriors threatened China from the north. In 221 B.C., the Chinese began to build a thousand-mile-long wall to protect their farms and cities from the Mongols. Over the centuries, the wall crumbled. Other walls were built, but still the raids went on.
In A.D. 1449, the Mongol army grew much stronger. More and more Chinese soldiers were killed. After one devastating defeat, a young Chinese emperor, Zhu Qizhen, was kidnapped by a Mongol prince. When news of the kidnapping reached the Chinese government, the people were seized by fear. Too weak to fight back, they decided to build a stronger wall. The building of the Great Wall, the last long wall, went on for the next two centuries.