Before the Christian era years were generally reckoned from the foundation of the city of Rome, or from the election of the emperor. With the establishment of Christianity they began to be reckoned from the birth of Jesus. An error in calculation by Dionysius the Younger (who in the 6th century introduced the present method of dating) made the birth of Christ coincide with the Roman year 754, whereas further studies have since ascertained that Jesus was born in 747 or 748, that is 6 or 7 years earlier than Dionysius had supposed.
From this results the curious fact that the Christian calendar which we now use, instead of starting from the birth of Christ, actually started 6 or 7 years after it. This explains why the date of the birth of Jesus is today reckoned to be 6 or 7 B.C.
As regards the public ministry of Jesus, it is generally held to have lasted little more than 2 years, in view of certain indications in the 4th gospel, which seems the most accurate on this score and speaks of 3 different Passovers. So, in all probability Jesus began his public ministry towards the beginning of 28 A.D.; his death occurred on the eve of the Passover of 30 A.D.
