Where did BC & AD come from?

The Year Without a Number

Author: Kenneth Dobyns
Cited From:  http://www.myoutbox.net/yearzero.htm

 Dionysius Exiguus, or in English “Little Dennis,” got a bad rap for inventing a calendar without a year zero. Dennis was the abbot of a monastery in Rome when, about 525 AD (by later reckoning), he was asked by Pope John I to develop tables to compute the proper date for Easter for any year. He was not asked to create a new calendar. Dennis was an intelligent and learned man, a member of the Roman curia, and one of the few men available who might have the mathematical ability to do the job (which required adding, subtracting and multiplying in Roman numerals).

For the purpose of this discussion, I assume the truth of the hypotheses apparently used by Dennis (he did not leave a clear indication of exactly how he did the job) —

1. The year begins on January first, or perhaps March 25, by the Roman calendar.

2. Jesus was born on December 25 (by tradition).

3. Easter is defined as the first Sunday after the full moon that falls on or after the vernal equinox. The vernal equinox is assumed to be always on March 21. The full moon is assumed to always be fourteen days after the new moon.

4. Jesus (according to one tradition) was crucified on Friday, March 25 and was resurrected on Sunday, March 27, which should meet the definition of Easter. See Bede, De tempore ratione (chapter 47), translated by Faith Wallis as The Reckoning of Time, Liverpool University Press (1999).

5. Jesus died after reaching age 33 but before reaching age 34 (based partly on Luke 3:23 and partly on accounts of his years of preaching). See Bede, De tempore ratione (chapter 47).

6. The calendar dates and days of the new and full moon recur on a grand cycle of 532 years by the calendar of Pope Hilary.

I realize that any or all of these hypotheses may be open to challenge, but my purpose is not to argue with Dennis, but rather to understand how he might have reached his conclusions. The conclusions themselves seem to be generally understood. What follows is a reconstruction of one possible path by which he might have reached his conclusions. Bede had access to a letter by Dionysius Exiguus entitled Epistola ad Bonifacium et Bonum explaining his calculations, and Bede seems to have accepted the following explanation of the logic of Dennis when writing his De tempore ratione.

The calendar in common use for many years in Rome numbered each year as “ab urbe condita” or “since the founding of the city [of Rome],” here abbreviated AUC. Dennis was working on his problem about 1278 AUC, later considered to be 525 AD. However, the more common dating system at the time was based on the years of Diocletian, who had been a notorious persecutor of Christians — and Dennis was determined not to use that system of years to chart the date of Easter. He decided to use the years of the Lord’s incarnation, which he then had to calculate.

He may have looked for a year which was 532 years after a range of dates approximately accurate for the crucifixion year which met the requirement that the defined Easter fell on Sunday, March 27, and found such a year in 1319 AUC.

532 years earlier than 1319 AUC was 787 AUC, when the same full moon dates would have occurred. So on March 25, 787 AUC, the assumed date of the crucifixion, Jesus would have been past his 33rd birthday but short of his 34th birthday. 33 years before March 25, 787 AUC was March 25, 754 AUC. This date was less than a year after the birth of Jesus, so Jesus was assumed to have been born on December 25, 753 AUC.

Dennis established January 1, 754 AUC (or perhaps March 25, 754 AUC) as the first day of the year 1 anno domini or AD, which was the year in which Jesus turned one year old. Thus the year in which Jesus was born was the year before 1 AD. This year had no number.

As a side issue, even assuming the truth and accuracy of the hypotheses, Dennis may have made an error in his calculations, which is now beyond correction. Faith Wallis has pointed out what has long been recognized — that Easter fell on March 28 in 34 AD or 787 AUC, and Bede knew it but did not openly comment on it. [Bede advised his reader to look for the March 27 date and give thanks to God if he found it.] The nearest dates on which Easter (by definition) fell on March 27 were 12 AD and 96 AD, despite the apparent assumption of Dennis that it fell on March 27 in 34 AD. An alternative belief was that resurrection occurred on March 25, which would match 31 AD or 784 AUC. That date would throw 1 AD back three years to 751 AUC. Of course the point is moot, since 1 AD is embedded in its time by now, whether or not that time is correct.

Dennis did not consider what to call the years before 754 AUC. He did not deal with the years before 1 AD. He did not establish BC years, did not use them, and apparently was not interested in them in connection with his calculations. Even if he had been inclined to use the term BC, I believe that he must have understood his calculations well enough not to call 753 AUC by the term 1 BC. He would not have said that Jesus was born in the year one before Christ. He did not have the use of the term “zero.” The term “zero” probably had not been invented anywhere in 525 AD and clearly was not known at that time in Europe.

But Dennis left plenty of wiggle room for the later introduction of a year zero. 753 AUC was the year before 1 AD and was also the year Dennis would have proposed that Jesus was born. It could easily have been renamed later as year zero. 752 AUC should logically have been the first year before Christ, or 1 BC.

So what happened?

Some would blame it on the Venerable Bede, who popularized Dennis’s work in his History of the English Church and People (perhaps more commonly entitled Ecclesiastical History of the English People.)

See Bede — A History of the English Church and People (731 AD) as translated by Leo Sherley-Price (Penguin edition), Book I Chapter 2 which includes the statement “Britain remained unknown and unvisited by the Romans until the time of Gaius Julius Caesar, who became Consul with Lucius Bibulus 693 years after the founding of Rome, and sixty years before the birth of our Lord.” (Apparently other manuscripts of Bede’s work say 593 instead of 693, but that date is clearly wrong.) Modern encyclopedias give this date as 59 BC rather than 60 BC.

Thus Bede was equating 693 AUC with 60 BC, or 752 AUC with 1 BC. Bede was correct in that he left 753 AUC unnumbered and available for later numbering as year zero. But Bede apparently made only one use in his writings of years BC or the equivalent. He did not use BC numbering in De tempore ratione. Bede was probably responsible for popularizing the numbering of years as anno domini or AD, but he had almost no effect on the numbering of years as BC.

A French astronomer, historian, priest and professor named Denis Petau (or, in Latin, Dionysius Petavius) introduced and popularized the regular use of BC terminology in 1627 in his De doctrina temporum. He allowed his historic dates to go from 1 BC directly to 1 AD. He lived in a period when he had full access to the use of zero — but he did not use it.

A somewhat revised and updated (and more importantly, translated) version of Petau’s work is accessible to English speakers as The History of the World or An Account of Time by Dionysius Petavius (London 1659), available on University Microfilms (Early English Books 1641-1700) 05018 reel 545. Petau used BC dating frequently in the history that he was presenting, but there are few places in his work where his assumptions as to the placement of 1 BC can be easily established. However, in the translated work, at Liber 2, Chap VII, he wrote that Romulus founded Rome 753 years before Christ or, in effect, 1 AUC equals 753 BC. By reciprocity, 753 AUC was equated with 1 BC. The potential year zero which had been left as wiggle room by Little Dennis disappeared at the hands of Denis Petau.

Blame it on Petau.

And, oddly enough, the only present-day group which has taken it upon themselves to insert a year zero into the calendar for their own use are the astronomers.

For questions and comments, please email me (Joshua).   Emails received are not received by or directed to the author of the article.

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