<human>:  Who built the Great Wall of China?
<bot>: The Great Wall of China was built by the Qin dynasty in 221 BC. The Qin dynasty was a dynasty of the Chinese people that ruled China from 221 BC to 206 BC. The Great Wall of China was built to protect China from invading forces from the north. The wall was made of stone and bricks and had a length of approximately 6,500 km.