That was 84 1 year BC, the Western Zhou Dynasty and the first year. The earliest chronology in the history of China, Chronology of Twelve Governors of Historical Records, began in this year, so this year is the beginning of the exact chronology in the history of China. Why this year? Sima Qian said that he consulted many documents when compiling history books, and there were many books about chronology, but their records after the first year (84 BC1) were consistent, which means that the exact chronology after 84 BC1can be determined. So, was there any historical record before 84 1? Yes, Sima Qian said that there was an exact date from the time of the Yellow Emperor. But different materials have different versions, and the real historical chronology cannot be determined. Therefore, based on the principle of seeking truth from facts, Sima Qian did not record them. With the development of history, those precious historical materials with dates before 84 BC1have gradually disappeared, and the earliest chronology handed down is only the chronology of the twelve princes in Historical Records, so we take 84 BC1as the exact date of our history.