The first dynasty in China was the Xia Dynasty, which was founded about 2 1 century BC, and now it is 2 1 century BC. They have been added for 4200 years, plus Shennong, Fuxi Shi and Huangdi before them. Yao. Yu et al. have a history of five thousand years.

There is another usage of the so-called AD: in the world, a certain year in history is designated as the first year of AD, and the previous year is BC. The bigger the number in BC, the older you get. The next few years are the post-A.D. years, also known as how many A.D. years. The bigger the number in the post-AD era, the more modern it is. 2006 is also called AD 2006.