In 525 AD, the Christian theologian Dionysus Ihiggs suggested that the year when Jesus was born should be the first year of the era, instead of the "Diocletian calendar" adopted by the Vatican at that time (the year when the Roman emperor Diocletian ascended the throne was famous for persecuting Christians, that is, in 284 AD, commonly known as the "martyrdom era"). Isis calculated that Jesus was born in 754 years after the founding of Rome, but later historians found his calculation wrong; At present, it is generally believed that the most reliable statement is that Jesus was born around 7-4 BC.
The idea was supported by the church, and this chronology was used by the church in 532 AD. At that time, the chronology of western countries was different. 1582, the Pope formulated the Gregorian calendar, which is highly accurate and internationally used, so it is called "A.D.". Since then, the year when Jesus was born is called the first year of AD. In history books, the year before the birth of Jesus is called "BC"; The year after the birth of Jesus was "after A.D." and was called "A.D.".
This chronological system began to be adopted by European countries. China adopted the Gregorian calendar month and day (19 12) one year after the Revolution of 1911, but at the same time adopted the year of the Republic of China. 1On September 27th, 949, the second of the four resolutions adopted at the first plenary session of China People's Political Consultative Conference was: "The Gregorian calendar in People's Republic of China (PRC) adopts AD".