Why was Jesus born ‘BC’?

The monk who invented AD

The years most of the world counts were set in Rome in 525 by a monk named Dionysius Exiguus. He came from Scythia, near the Black Sea, translated Greek church documents into Latin, and was known as Exiguus, “the Small,” a name usually taken as a mark of humility. That year he drew up new tables for finding the date of Easter. The tables he inherited, from Alexandria, numbered the years from the accession of the emperor Diocletian in 284, the emperor of the last great persecution. Dionysius did not want to keep a persecutor’s memory alive in the Church’s calendar. So he numbered his years “from the incarnation of our Lord Jesus Christ,” and his table began with the year 532. Egypt’s Coptic Church still counts from Diocletian, as the Era of the Martyrs.

Where the count went wrong

Dionysius never explained how he fixed the year of the birth, and scholars still argue about his arithmetic. But the Gospels hold a clue that his count does not fit. Matthew and Luke both set the birth in the reign of Herod the Great (Luke 1:5).

Now when Jesus was born in Bethlehem of Judea in the days of King Herod, behold, wise men from the east came to Jerusalem,

Herod outlived the birth by a while. Matthew has him order the killing of Bethlehem’s boys “from two years old and under” (Matthew 2:16), and then die while the family is still in Egypt.

But when Herod was dead, behold, an angel of the Lord appeared in a dream to Joseph in Egypt,

The Jewish historian Josephus places Herod’s death after an eclipse of the moon and before a Passover, which most historians match to the spring of 4 BC; how Herod died has the details. A birth a year or two earlier gives the usual estimate: about 6 to 4 BC.

How “before Christ” caught on

At first Dionysius’s years lived mostly in Easter tables. The man who made them popular was the English monk Bede. His Ecclesiastical History of the English People, finished in 731, dated events by the year of the Lord throughout, and it was copied all over Europe. Bede even counted backward: Julius Caesar, he wrote, came to Britain in the sixtieth year before the incarnation of the Lord. Caesar actually landed in 55 BC, but the backward count had begun. Over the following centuries the year of the Lord spread through the chronicles and charters of Christian Europe.

No year zero

One more quirk matters for the arithmetic. There is no year 0. The count goes straight from 1 BC to AD 1, because neither Dionysius nor Bede used a zero. So a child born in 5 BC turned ten in AD 6, not AD 5. Astronomers later added a year 0 to make their sums easier; historians never did. It is also why sticklers insisted that the third millennium began on January 1, 2001, not in 2000.

AD, BC, BCE, CE

AD stands for Anno Domini, Latin for “in the year of the Lord.” BC is English: “before Christ.” Many writers now prefer BCE and CE, “before the Common Era” and “Common Era,” to avoid a religious label. The numbers stay the same: Dionysius’s numbers, miscount and all. So the calendar keeps its odd result. By its own count, Jesus was born a few years before Christ.