In 221 BC, Ying Zheng, first emperor of the Qin Dynasty, put an end to the 250-odd years of rivalry among the independent principalities during the Warring States Period, and established the first centralized, unified, multi-ethnic feudal state in Chinese history - the Qin Dynasty (221-206 BC). He was called Qin Shi Huang or "First Emperor of Qin." He standardized the written script, weights and measures, and currency, and established the system of prefectures and counties. The sovereigns of the next 2,000-odd years followed the feudal governmental structure established by him. He mobilized more than 300,000 people over a period of a dozen years to build the Great Wall, which stretches for 5,000 km across northern China. Qin Shi Huang had the work on his enormous mausoleum started early in his reign. The terracotta warriors and horses of the "underground army" guarding the mausoleum, unearthed in 1974, amazed the world. The 8,000 vivid, life-sized pottery figures, horses and chariots have been called the "Eighth Wonder of the World."