The Myth of the Year 0

by Cesare A. Galtieri

With the approaching of the year 2000 there has been a resurrection of the discussion about the start of the "third millennium" being on January 1, 2000 or January 1, 2001. A similar discussion occurred just prior to the year 1900, about the start of the "20^th century". Part of the discussion is the repetition of the myth that "there was no year 0". We will attempt to clarify the origin of the myth and, maybe, we might put it to rest. To make our point very clear we will "start at the beginning", so that the various steps can be traced reasonably clearly.

The Year 0 AD

During the Middle Ages there were many different systems for establishing the time of specific events. Sometimes people referred to events as having occurred "in the third year of king such-and-such", or " in the sixth year of pope such-and-such", or relative to certain special cycles. The confusion was particularly annoying to the christian establishment because the setup of the date of Easter was made according to certain tables, but the reference point of those tables was not clear.

One of the more consistent ways of keeping track of the passage of years was the counting of the years ab urbe condita (AUC), meaning the number of years since the "traditional" foundation of Rome. That accounting had not been truly kept since the foundation of Rome. It was setup late in the time of the roman republic on the basis of the (reasonably good) records of the sequence of roman consuls and the somewhat arbitrary estimate of the length of the roman monarchy, which was set to 244 years. Once established, the accounting was maintained reasonably accurately, at least since the later years of the republic. So we believe that we know with accuracy that Julius Caesar was born in the year 654 AUC and died in the year 710 AUC.

In the year 1278 AUC, the christian Pope John I asked the monk Dionysius Exiguus to straighten out the chronology associated with the establishment of the date of Easter. Dionysius came up with the idea of counting the years from the date of the birth of Jesus of Nazareth, the traditional founder of the christian religion. According to his accounting, he decided that the birth had occurred in the year 753 AUC. He then renamed the year 754 AUC as the year 1 Anno Domini (AD).

Once the equivalence:

754 AUC = 1 AD

was established, obviously the correspondence of every other year is equally set. So, for example, the year in which Dionysius came up with the idea (1278 AUC) became automatically the year 525 AD.

In the times of Dionysius the role of the "zero" in arithmetic was not understood in the western world. Furthermore, the notion of negative numbers was totally foreign to the medieval mind. In order to account for the years prior to the year 1 AD, the year 753 AUC was renamed as the year 1 Before Christ (BC). The accounting for years preceding that was done in reverse order, i.e. the year 752 AUC was called the year 2 BC, and so on.

Today we understand the meaning of "zero" and of negative numbers. Therefore, today we know that when the correspondence between the year 754 AUC and the year 1 AD was made, it meant that automatically, the correspondence was also made for all other years. In particular:

755 AUC = 2 AD
754 AUC = 1 AD
753 AUC = 0 AD
752 AUC = -1 AD
751 AUC = -2 AD

and so on. The confusion comes from the lack of realization that the accountings of the dates according to the "AD" and the "BC'" denominations are two separate accountings, with the correspondence between the two being obviously

0 AD = 1 BC
-1 AD = 2 BC

and so on.

In order to make the point more clear let me restate the obvious. Once Dionysius established that he would rename the year 754 AUC as the year 1 AD, he did not have the choice of renaming any other year, according to the AD system. All years, preceding or following the year 754 AUC, were automatically renamed, including the fact that the year 753 AUC became the year 0 AD. The fact that he did not recognize that fact has to do with the state of the understanding of arithmetic in the year 1278 AUC.

Unfortunately later historians, probably down to the present, have had no better understanding of arithmetic than Dionysius had. If they had it, they would have started to use the negative AD accounting to refer to dates prior to 753 AUC. So, we would read in history books that Julius Caesar was born in -99 AD (instead of 100 BC) and that he died in the year -43 AD (instead of 44 BC). This would have clarified the issue once and for all. Unfortunately, they did not. But the fact that they kept using the "BC" method to refer to dates prior to the year 754 AUC does not change the fact that the year 753 AUC is the year 0 AD.

It should be noted that the fact that the year 753 AUC has not been "called" the year 0 AD, either in its own time or later, does not mean anything. Since the AD accounting was not invented until the year 525 AD, none of the years preceding that one was ever called by its AD equivalent in its own time. Furthermore, the AD accounting did not become actually in general use in the christian world until around the year 1000 AD. Therefore if we should take into account what the years have been "called", none of the years before the year 1000 AD were "properly called" by their AD number.

The Origin of Time, Centuries and Millennia

Time is a scalar quantity, i.e. is measured by a real number. In order to have a consistent measurement of "real time" we need to set up two major parameters, namely the units by which time is measured and the origin of the scale, i.e. the point in time that we set as "time zero". There is very little discussion (fortunately!) on the units that we are supposed to be using. Everybody by now uses seconds, minutes, hours and days. Different cultures use different definitions of months and years, but we are here only concerned with thir uses in the context of the so-called "Gregorian Calendar" and there is no issue in that context. The main issue is the setting of the point in time which is defined as "time zero".

The resetting of the year 753 AUC as the year 0 AD also determines the setting of "time zero" as the midnight between December 31 of the year 752 AUC and January 1 of the year 753 AUC. So the day of January 1 of the year 0 AD was the "first day" of the "AD era". The year 0 AD was the "first year" of the AD era. The first one hundred years of the AD era, i.e. the "first century AD" is the period between January 1 of the year 0 AD and December 31 of the year 99 AD. Notice that for centuries before the year 0, the years -100 AD to -1 AD would then be considered the "1^st century before AD" and so on.

This is consistent with the standard nomenclature used by most historians that consists of naming a century by dropping the last two digits of the AD denomination and adding 1 to what is left. In other words, the years from 0 to 99 belong to the "1^st century AD"; the years from 100 to 199 belong to the "2^nd century AD" and so on, with the years from 1900 to 1999 would belong to the "20^th century AD".

Similarly the years from 0 to 999 would belong to the "first millennium AD" and the years from 1000 to 1999 would belong to the "second millennium AD" and so on. I believe that this is going to be the most common interpretation and that therefore the overwhelming majority of the people of the world will celebrate the "beginning of the third AD millennium" at the midnight between December 31, 1999 and January 1, 2000.

The Current Era (CE)

In recent times there has been a highly desirable attempt to substitute the expression Current Era (CE) for the expression AD. There are two good reasons for this. The first is political. As the AD accounting has become the standard of the world, it is somewhat offensive to non-christian groups to think in terms of christian mythology. The expression "CE" is a "neutral" one from a religious point of view. The second reason has to do with historical accuracy. It is well known that Dionysius's accounting of the birth of Jesus of Nazareth created an inconsistency between known facts and the traditional christian account of the birth. If, as reported in traditional christian accounts, Jesus of Nazareth was born during the reign of Herod, then the birth must have occurred no later than the year 750 AUC. It is now commonly accepted that if we take the christian accounts literally, the birth of the Jesus of christian legend would have occurred in the period 748-750 AUC (i.e -5 to -3 AD), or 6 to 4 years "Before Christ"!

In the years just before the year 1000 AD, there developed a fear, in certain parts of the christian world, that the number "1000" was a magic number and that something "significant" (and really bad) would occur in that year. Now that the year 2000 is approaching, similar conjectures are revived, mainly jocularly, but sometimes seriously by some fringe christian cults. The irony of the fact is that presumably the christian god does not make the same historical errors that Dionysius made. If something special was to have occurred in the 2000^th year since the birth of Jesus of Nazareth, then this would have occurred in the years 1995-1997 or thereabout.

Nothing happened, so we can relax and enjoy the beginning of the third CE millennium on January 1, 2000 CE