When did it start in BC?

AD is a kind of chronology. We commonly say that 20 1 1 year is 20 1 1 year from the first year of AD, that is to say, before 20 1 1 year. It is said that the year when Jesus Christ was born was the first year of AD. From the 6th century to the10th century, it gradually became the common era of Christian countries, so the original Christ was also called the "Christian era". Later, it was shared by most countries in the world, so it was renamed "A.D.", which is usually expressed in A.D. (the abbreviation of Annodomeni means "the year of the Lord"). In history books, the year before the birth of Jesus is called "BC", which is usually written by BC(Before Christ), meaning "before Christ". The year after the birth of Jesus is "After A.D.", or "A.D." for short. The first year of AD, equivalent to the first year of China Xihanzi Yuan.