Posted by Dr. Taylor Marshall 
The following post is derived from Dr. Marshall's new book The Eternal City: Rome & the Origins of Catholic Christianity:
As you know, B.C. refers to “before Christ” and it is therefore confusing to hear scholars say that Christ was born in 4 B.C. This would mean that Christ was born four years before Christ. However, recent and more precise chronological studies have validated the traditional date of Christ’s birth at December 25 in 1 B.C.[i]
As way of background, the dating of B.C. (before Christ) and A.D. (anno Domini or year of the Lord) derives from the calculations of the Dionysius Exiguus. Exiguus meanslittle, so he is often called Dionysius the Little. Dionysius was a Scythian monk living in Rome. He died in about A.D. 544. Incidentally, when you write dates, B.C. goes after the number and A.D. goes in front of it. For example:
754 B.C.
or
A.D. 1492
In Rome, Dionysius worked with the best Roman records and Church documents to compute the birth of Christ. This new computation divided time before and after Christ. Dionysius did not include a year zero. December 31 in 1 B.C. would have passed to January 1 in A.D. 1.
Now Dionysius identified Gabriel’s annunciation to the Virgin and the incarnation of Christ in the womb of the Blessed Virgin Mary on March 25 in the year 1 B.C. He recognized the birthday of Christ as being December 25 in the year 1 B.C. The circumcision of Christ, eight days after His birth, was on January 1 of A.D. 1. His crucifixion was in the year A.D. 33.
The Venerable Bede took up the dating scheme of Dionysius the Little in his Ecclesiastical History of the English People, and the rest is history. We still use his dating system to this day—B.C. and A.D.
Doubts over the birth year of Christ arose in the 1600s. Scholars became aware of the chronology provided by the Jewish historian Josephus. Josephus places the death of King Herod the Great in what Dionysius called 4 B.C. Since Herod tried to kill the infant Christ, then it would necessarily be the case that Christ would be born before the death of Herod. If Herod died in 4 B.C., then Christ would need to be born before 4 B.C. And so, ever since the seventeenth century, people have been claiming that Dionysius got it wrong and that Christ was born four years before Christ.
What do we make of all this? Well, either Josephus is correct or Dionysius is correct. Both cannot be right. Until recently most scholars agreed with Josephus because: A) Josephus lived in the century of Christ, B) Josephus was Jewish, and C) Josephus was a professional historian. Dionysius was just a monk living in Rome over five hundred years later.
However, there is now good reason for believing that Josephus got it wrong. Further studies of Josephus reveal that he was most certainly not consistent or accurate in dating several key events in Jewish and Roman history. In fact, Josephus contradicts verified history, the Bible, and even his own chronology about one hundred times. His dates are not very accurate. The French archaeologist, jurist, and historian Theodore Reinarch was one of the first to document the many factual and chronological errors of Josephus. Reinarch’s translation of Josephus is steadily interrupted by comments such as “this is a mistake” or “in another book his figures are different.”[ii]
The following is an example of the poor chronology of Josephus. Josephus records in his Jewish War that Hyrcanus reigned for thirty-three years. Yet in his Antiquities of the Jews, that Hyrcanus reigned thirty-two years.[iii] Yet in another place in his Antiquities, Josephus says that Hyrcanus reigned only thirty years. That’s three contradictory claims—two in the same book!
In his Jewish War, Josephus records that Aristobulus set the diadem on his head 471 years after the exile. Yet in his Antiquities, he says it was 481 years, a ten-year difference. By the way, modern historians now know that it was 490 years. Josephus is wrong on all accounts.
More examples could be supplied. The fact is that Josephus was sloppy with dates, especially when they regarded monarchs. So let us take a look at the dates he gives for King Herod. We discover that Josephus actually gave two contradictory dates for the death of Herod—4 B.C. and A.D. 7 or 8.
Josephus writes that Herod captured Jerusalem and began to rule in what Dionysius would call 37 B.C., and that Herod lived for 34 years after this. If you do the math, this means that Herod died in 4 or 3 B.C. Scholars site this as the authoritative proof that Jesus was born before 4-3 B.C.
However, Josephus records a different dating for the death of Herod elsewhere. In his Antiquities, Josephus writes that Herod was fifteen years old in what we would call 47 B.C. when Caesar appointed Hyrcanus as ethnarch.[iv] But, twice elsewhere Josephus states that Herod was seventy years old when he died. So if Herod was 15 in 47 B.C., that means he died at age 70 in either A.D. 7 or A.D. 8.
We have a serious discrepancy in the dates of Josephus—a window of more than ten years. Moreover, who really knows if either number is accurate given his mistakes on other historical dates?
Why is this important? It reveals that we should not allow Josephus to have the last word on the chronology of Christ. Josephus’ dating of Herod’s death to 4 B.C. is truly only one version of his calculations. Why not use his date of A.D. 7 or 8? It is rather arbitrary for modern historians to endorse the date of 4 B.C.
The best way to date Herod’s death is by focusing on the testimony that Herod died a few months after a well-observed lunar eclipse. With modern astronomical models, we know that such a lunar eclipse occurred at Jerusalem before sunset on December 29 in 1 B.C. This would mean that Herod died sometime after A.D. 1. This lines up perfectly with the chronology of Dionysius the Little. This means that Christ was born on December 25 of 1 B.C. and that He was circumcised on January 1 of A.D. 1.
Our Calendar is perfectly accurate!
