Who built to protect the empire from Northern invaders in China?

The Great Wall of China was built to protect the empire from northern invaders, particularly the Mongols and other nomadic tribes. Construction began as early as the 7th century BC, with significant contributions made during the Qin Dynasty (221-206 BC) and later during the Ming Dynasty (1368-1644). The wall served as a formidable barrier and a means of border control, military defense, and trade regulation. Its construction involved numerous workers, including soldiers, peasants, and prisoners.