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Calendar Systems Part 3 - Origin of the BC-AD Dating System

In part 2, we explored the development of various calendar systems within the political and historical context of the major nations during Biblical times and the early church period.  In part 3, we look at the origin and the eventual acceptance of our modern BC-AD (Anno Domini) dating system.

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Origin and Significance of BC-AD Dating System

Throughout the previous parts of this article, we’ve dated most events using the “BC” year designation.  Obviously, as most of our astute readers would notice, we won’t find any documents dated with BC by their original author (or even with AD in the first few centuries AD).  The BC-AD dating system did not exist prior to the sixth century AD, but since it is now the almost universally accepted dating system, and since dating systems can be applied to any calendar system (see the “Calendar Components” chapter in part 1), we can back-date all previous events for standardization and simplicity (see the “Closing Thoughts” chapter in part 5 for back-dating challenges).  After all, dating an ancient event within its original calendar dating system would mean nothing without at least a common point of reference to our modern dating system.

We now examine the meaning of BC-AD, including how and why it come about.  “BC” and “AD” are designations given to identify the years within the calendar dating system that is based upon the birth of Christ as its point of origin.   Every so often, we hear someone pose the question, “If BC denotes ‘Before Christ’ and AD signifies ‘After Death’, how do we number the years between his birth and death?”  This question stems from a somewhat common misconception regarding the terms of our modern dating system.  The expansion of BC is correct, but “AD” actually is an abbreviation of the Latin “Anno Domini” translated “Year of our Lord” which refers to the year of Christ’s birth.

Origin of the Anno Domini Dating System

The BC-AD or the Anno Domini calendar dating system came about almost as a byproduct of the historical debate over the dating of Easter.  A full discourse on the disagreements over which day to celebrate Christianity’s most important holiday (which continue even today) is beyond the scope of this article, but we’ll hit the brief highlights.

The original Easter of course, is based on the crucifixion of Christ, which we can date on the 14th of the Hebrew month of Nisan (aka Aviv prior to the exile), in the year 30 or 33 AD (see “Dating the Life of Christ” - in progress).  According to Eusebius' Church History, variances over the date of celebration were present within the very next generation after Jesus and the apostles.  Eusebius writes of a letter composed by the early church father Irenaeus (130–202 AD) that records his teacher Polycarp (~70-155 AD) of Smyrna, and disciple of the Apostle John, attending a meeting to discuss the date of Easter.  At the time, many of the Asian Christians held the celebration on Nisan 14, while most others observed Easter on the Sunday that fell within that week since the Lord was resurrected on a Sunday.

At the First Council of Nicaea (325 AD), it was agreed that the date for Easter be divorced from the Hebrew calendar and the Jewish Passover.  It was further decided to observe the holiday on the Sunday after the first full moon on or after the day of the vernal (or Northern Spring) equinox.  The council however, did not issue explicit instruction regarding the method of computation.  The Alexandrian Easter tables, based upon a 19-year cycle, became the dominate method, but several others continued to be in use such that, by the end of the fourth century, the celebrations varied each year by as much as five weeks.

Many unsuccessful attempts were made over the next hundred plus years to harmonize the Easter date among the various churches.  Finally in 525 AD under the direction of Pope John I, Dionysius Exiguus, a Scythian monk and scholar living in Rome, published new Easter tables based upon the Alexandrian computations, but converted from the Alexandrian to the Julian calendar.  These computations remained in use for the Roman church and throughout Western Europe until the Gregorian calendar reform about a thousand years later.  The Roman Catholic Church switched in 1583 AD and most Protestant churches adopted the Gregorian Easter either prior to, or over the next hundred years.  At this time, many European protestant churches were using astronomical Easter computations based on tables developed by Johannnes Kepler, arguably the most important astronomer of the scientific revolution and the father of “celestial mechanics” which helped explain the planetary motions.  Like most scientists who helped issue in the era of modern science, Kepler gave the glory to God for all his achievements.

Yet even with the longevity of the Dionysius Easter tables (his computations are still used in many Eastern and Oriental Orthodox churches today), they pale in comparative popularity with his related development of a new calendar dating system.  At the time, some calendars were dated by the aforementioned AUC system (based on the founding of Rome), but in the most commonly used system, calendar years were dated from the first year of the reign of Roman Emperor Diocletian (284 AD) who ushered in the bloodiest persecution of Christians (~303-311 AD) ever sanctioned by the empire.  Diocletian's attempt to exterminate the believers failed, and Christianity even became a “legal” religion less than 15 years later under Emperor Constantine, and later became the state religion of the Roman Empire when Emperor Theodosius I issued the Edict of Thessalonica in 380 AD.  Still, it must have been troubling to many believers to utilize dates based upon Diocletian’s reign.

Thus, the decision was made to abandon the pagan dating system and to replace it with a Christian-based structure.  Consequently, Dionysus anchored his dating system by counting years from the Incarnation of Jesus the Christ (ab incarnatione Domini nostri Jesu Christi).  In his attempt to calculate the year of the Messiah’s birth, he used Bible facts such as Jesus being baptized in Tiberius’ 15th year (Lk 3:1) and that he was about 30 years old at the time (Lk 3:23).  Also considering available historical and scientific data, he estimated that Jesus was born in 753 AUC.  He then designated the following year (754 AUC) as 1 AD.  There was no year zero, so the period from January of 2 BC to January of 2 AD is only three years instead of four.  The absence of a year zero is also why the 21st century actually began on January 1, 2001 instead of in 2000 as many people supposed.  It is unclear whether Dionysius included the negative “BC” years in his system or if they were added by Bede in the eight century (see next chapter).

Despite his abandonment of the old dating system, Dionysius established a correlation with the Diocletian years for those who continued to use the old system (the Anno Domini dating system would not gain considerable popularity for hundreds of years).  The previous Easter tables comprised the nineteen-year period ending in 247 Anno Diocletian.  Dionysius renewed the table for another nineteen years, beginning with 248 Anno Diocletian but also specifying the years as 532-550 Anno Domini (AD).

It was later discovered that Dionysius was slightly off regarding his calculation of the year of the Incarnation.  We observe from the account of Herod and the Magi in Matthew chapter 2 that Mary and Joseph took Jesus to Egypt after his birth to avoid Herod’s attempt to kill the child.  This lets us know that Jesus was born while Herod was still alive.  The family returned, settling in Nazareth of Galilee after Herod’s death.

Now, we can estimate the death of Herod by comparing the writings of the Jewish historian Flavius Josephus and improved astronomical data.  In his Antiquities of the Jews, Book XVII, Chapter VI, Josephus places Herod’s death shortly after an eclipse of the moon.  Additionally, in Josephus’ Wars of the Jews, Book II, Chapter I, he writes that Archelaus made a funeral feast at Passover for his father Herod, thus placing his death in a short period between a lunar eclipse and Passover.

From the NASA Lunar Eclipse Page, we find eclipses occurred on March 23, 5 BC, March 13, 4 BC and January 10, 1 BC.  Based on this and other evidence (see “Dating Events in the Earthly Life of Jesus” – in progress), historians have traditionally favored the Spring of 4 BC as the most likely date of Herod's death, although the 1 BC date has gathered increased support in recent years.

Since, in his attempt to kill Jesus, Herod ordered all males in the vicinity of Bethlehem who were two years and under slain, the most likely year of Jesus’ birth is thought to be in either 6 or 5 BC (3 or 2 BC for those who favor the 1 BC date for Herod’s death).  Yet even though Dionysius’ Incarnation estimate was off by a few years, his calendar dating system would become the recognized standard, but not right away as we'll see in Part 4 – Adoption of the Anno Domini Dating System.

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