It was Dionysius' job to help make this happen and he tried to do so by reforming the calendar; calculating the date of Jesus' birth was a means to this end, not an end in itself.
Using the four gospels to determine Jesus' birth, however, is problematic since the Gospel of John does not agree with the other three and Matthew, Mark, and Luke do not always agree with each other regarding significant events. Cargill explains: According to the Gospel of Matthew, Jesus was born during the reign of Herod the Great.
The use of BCE/CE, opponents claim, is offensive to Christians who recognize time as dated up to, and away from, the birth of Jesus.
This method of dating was continued by the Romans who counted their years according to three different systems in different eras: from the founding of Rome, by which consuls were in power, and by which emperors ruled at a given time.Julius Caesar (100-44 BCE) reformed the calendar and renamed the months during his reign (49-44 BCE).This calendar remained in use, with periodic revisions, until 1582 CE when Pope Gregory XIII instituted the Gregorian Calendar still in use in the present day.He seems to have arrived at his calculations through a reliance on scripture and known history of the time to create a calendar which would be acceptable to both the western and eastern churches of the time in harmonizing the celebration of Easter.Dionysius never makes the claim that he knew the date of Jesus' birth and no later writer makes that claim for him.