You can believe what you like but my information tells me that in 525, Pope John I commissioned Dionysius Exiguus (“Dennis the Short”) to calculate the date of Jesus’ birth.
Dionysius was a Ukrainian monk and a respected scholar, mathematician and astronomer. Working from the old Diocletian calendar that measured time from the (mythical) founding of Rome, Dionysius created a new calendar based on the birth of Jesus.
As he explained at the time, “We are unwilling to connect our cycle with the name of an impious persecutor (i.e., Diocletian), but have chosen rather to note the years from the incarnation of our Lord Jesus Christ.”
Hence, the designation Anno Domini (A.D.) — “In the Year of our Lord.”
Inexplicably, although the entire Western world eventually adopted the A.D. system, historians and chronologers continued to date the years before Christ using the same dating systems of antiquity until the 18′h century, when it finally became common practice to refer to these years as “B.C.” — Before Christ.”
Using the gospels of Matthew and Luke as guides, Dionysius calculated that Jesus was born in the 753rd year of the old Roman calendar. His calculations were probably off by a couple of years as the best evidence indicates that Jesus was probably born sometime between December of 3 BC and February of 2 B.C.
According to the gospels, Jesus was born when Herod the Great was king of Judea, and Herod probably died in 1 B.C.