Who built the Great Wall of China and why?

The Great Wall of China was built over many centuries by various Chinese dynasties, with the earliest sections constructed as early as the 7th century BCE. However, the most famous and extensive parts of the Wall were ordered by Emperor Qin Shi Huang, the first emperor of a unified China, around 221 BCE. He connected and expanded existing walls built by earlier states to create a more formidable defense system. Later dynasties, especially the Ming Dynasty (1368–1644), further rebuilt, reinforced, and extended the Wall to protect against invasions. The primary purpose of the Great Wall was to defend Chinese states and empires from invasions and raids by nomadic tribes from the north, such as the Xiongnu and later the Mongols. Besides military defense, the Wall also served to control immigration and emigration, regulate trade along the Silk Road, and assert the power and reach of the Chinese emperors. While it was not a continuous wall at first, over time it became a massive fortification symbolizing China's strength and ingenuity.