<human>:  Why did the Chinese build the Great Wall?
<bot>: The Great Wall was built to protect China from invasions from the north. The Great Wall is a massive wall that stretches from the Pacific Ocean to the Gobi Desert. It was built over many years starting in the 4th century BC. The Great Wall is made up of stone and brick and was constructed by thousands of workers. The Great Wall is a symbol of China's strength and power, and it is a popular tourist attraction.