The "impossible" would be the unification of China, which had been disunited for some time. China had gone through a period of intense turmoil, known as the "Period of the Warring States." This time frame had been so devastating that many thinkers of the time began to ponder the nature of society itself. A number of important Chinese philosophies developed from this time of thought, including Legalism, Daoism, and most importantly, Confucianism.
Qin Shihuangdi proclaimed himself the first true Emperor of China in 221 B.C.E. He and earlier Qin rulers were able to consolidate rule by taxing agricultural produce, and using the taxes to equip a massive army which fought with iron weapons. Their opponents weapons were no match for iron. Qin was able to rule from a central location without reliance on the nobility, whom he ignored. He dismantled military forces who might have threatened him and tore down their fortresses. He also standardized weights, measures, and currency and most importantly the written Chinese language.
Qin predicted that his regime would last a thousand years. In fact, it ended with his death in only fourteen years. He was heavy handed in dealing with dissent, and upon his death, rebellions broke out which overwhelmed his government. He did, however, lay the groundwork for the Han dynasty which followed and lasted until 220 C.E.
Qin did leave a magnificant tomb for prosperity which can still be viewed. It was constructed by over 700,000 workers, many of whom were executed and buried with him. Among the items in the tomb was a complete army of 15,000 life sized soldiers constructed of terra cotta. To prevent robbers from raiding his tomb, a series of traps including spring loaded cross bows were placed in the tomb to keep it secure.