The first dynasty of Ancient China, the Shang Dynasty (商朝), has been carbon dated through Turtle shells with writing on them to back to about 1500 BC. They say China began as city-states in the Yellow River valley. At the end of the Zhou Dynasty lived the greatest Chinese philosophers: "Kong Fuzi", founder of Confucianism, and Laozi, founder of Daoism. The Qin (秦) emperor Qin Shi Huang in 221 BC created the first centralized state in China based on his political philosophy of legalism and made everyone write the same way. He fought against "Confucianism". He also started a precursor of the Great Wall. In 202 BC the Han Dynasty took over and developed an empire of similar strength as the Roman Empire and towards the end of its rule influenced by India introduced Buddhism in China.