When Did the New Millennium Begin?
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The short answer is:

If you use the Gregorian Calendar and start the first millennium with the year 1 AD then the third millennium began with the year 2001 AD. But if you use the Common Era Calendar, in which years are numbered -2, -1, 0, 1, 2, ..., and you begin the first millennium with the year 0 CE then the third millennium began with the year 2000 CE. You have a choice. And if you opt for the Common Era Calendar you no longer have to put up with the smug assertion that "there was no year zero (so the new millennium began in 2001)". There was no year zero when Pope Gregory XIII introduced the Gregorian Calendar in the 16th Century but there certainly is one now (and in the future), and the new millennium in the Common Era Calendar began in 2000 CE.

See also: Re: Millennium Article and Re: .../newmill.htm

It is also not irrelevant to point out that the recent New Year celebrations on 31st December 2000 were a rather ho-hum affair compared to the spectacular and almost delerious celebrations around the world on 31st December 1999 / 1st January 2000. Only a few astronomers, pedants and Christian clergy tried to convince us that 1st January 2001 was the big day, but most of us were unconvinced, and rightly so.

For the long answer please continue reading.

This article was originally written in January 1999, and so is written from the perspective of an approaching millennium rather than one just begun.


"When Does the New Millennium Begin?" is a question which arouses great controversy, divides families and causes sleepless nights. I hope that this article will dispel the confusion which surrounds this question, and allow the reader to make an informed choice.

Most experts in calendrical matters will answer that the new millennium begins on the 1st of January in the year 2001, despite the fact that this answer is not the one that most people would like to hear (because, despite what the experts say, they intend to celebrate the new millennium on 1st January 2000). So let us first look at why the experts generally maintain this view. Then we can consider whether we wish to agree with them.


The calendar in common use comes down to us from the calendrical reform of 1582 by Pope Gregory XIII (for more information see The Julian and the Gregorian Calendars). In the Gregorian Calendar years are numbered "Anno Domini", meaning "in the year of Our Lord" (that is, Jesus Christ). This system of numbering years was instituted in the year 525 by the Roman abbot Dionysius Exiguus. In the Roman Empire years had been numbered according to the system of counting years from the founding of the city of Rome, or from the beginning of the reign of some emperor. Dionysius, as a Christian, believed that this pagan system should be replaced by one in which years were numbered by counting from the year in which Jesus was born. As the U.S. Naval Observatory tells it:

Many initial epochs have been used for calendrical reckoning. Frequently, years were counted from the ascension of a ruler. For a calendrical epoch to be useful, however, it must be tied to a sequence of recorded historical events. This is illustrated by the adoption of the birth of Christ as the initial epoch of the Julian and Gregorian calendars. This epoch was established by the 6th century scholar Dionysius Exiguus who was compiling a table of dates of Easter. Dionysius followed previous precedent by extending an existing table to cover the 19-year period 228-247, reckoned from the beginning of the reign of Emperor Diocletian. However, he did not want his Easter table "to perpetuate the memory of an impious persecutor of the Church, but preferred to count and denote the years from the Incarnation of our Lord Jesus Christ." To accomplish this he designated the years of his table Anni Domini Nostri Jesu Christi 532-550. Thus, Dionysius' Anno Domini 532 is equivalent to Anno Diocletiani 248, so that a correspondence was established between the new Christian Era and an existing system associated with historical records. What Dionysius did not do is establish an accurate date for the birth of Christ. While scholars generally believe that Christ was born a few years before AD 1, the records are too sketchy to allow a definitive dating.The 21st Century and the 3rd Millennium - When Will They Begin?

Dionysius's estimate of the year of Jesus's birth was off by about five years (Jesus was born in 6 B.C. at earliest, when the Emperor Augustus issued a decree for a census, and in 4 B.C. at latest, when Herod died). But this was not generally known for over 1400 years after Dionysius's time, and for Christian Europe throughout the Middle Ages and into modern times years were reckoned by this system of counting years from the first (the year in which Jesus was born, or rather, was believed to have been born) onwards in an unbroken succession. This succession was not interrupted by the Gregorian reform, which, although it removed ten days from the calendar, did not change the system of numbering years.

Since the "Anno Domini" system did not come into effect until the 6th Century A.D. it is artificial to speak of the years 1 A.D., 100 A.D., etc., because people living at that time knew nothing of this system of numbering years (since it had not then been invented yet). Furthermore the Romans in the reign of Augustus (27 B.C. to 14 A.D.) were somewhat lax in the proper observance of leap years. But we can project backwards (and forwards) from 525 A.D. by representing the succession of years by the series of natural numbers: 1, 2, 3, ..., 100, ..., 500, ... Then we can say that the period from 1 A.D. through 10 A.D. (including both years) was a period of ten years (since there are ten numbers in the series 1, 2, ..., 10). Similarly from 1 A.D. through 100 A.D. is a period of 100 years, and from 1 A.D. to 1000 A.D. is a period of 1000 years.

The word "millennium" means "a period of 1000 years" so we can conclude that the period from 1 A.D. through 1000 A.D. (including both years) constituted one millennium, and in fact, the first millennium of the Christian era. So the second millennium of the Christian era begins with the year 1001 A.D., or more exactly, on 1st January 1001 A.D. And the third millennium of the Christian era begins on 1st January 2001 A.D. So for Christians — or at least, for all who adhere to the Christian system of numbering years — the answer is clear: The new millennium begins on 1st January 2001 A.D.


However, this is not the end of the matter, because the "Anno Domini" system of year numbering has a major flaw, namely, it may be OK for years since 1 A.D., but what happens when we consider earlier years? As is well known, such years are numbered in reverse order, and designated as years "Before Christ". Thus the year immediately before 1 A.D. is designated 1 B.C., and the series extends backwards: 2 B.C., 3 B.C., etc.

With the rise of modern scholarship, particularly astronomy, archaeology and chronological studies, this system was felt to be inadequate for scientific purposes. For one thing it does not lend itself to calculation using dates. For example (a very simple one), how many years elapsed between 1st January 6 B.C. and 1st January 6 A.D.? Twelve years? No. The answer is not obvious (and still less obvious if we consider longer periods such as that from 535 B.C. to 481 A.D.).

So astronomers and chronologists decided to number years by representing the succession of years by the doubly-infinite series of positive and negative numbers: ..., -3, -2, -1, 0, 1, 2, 3 ... This is called the "astronomical" system of numbering years. In this system years from 1 onwards have the same numbers as years A.D. (year 1 = 1 A.D., and so on), but years  B.C. are related as follows: The year 0 in the astronomical system is the year 1  B.C., and the year -n in the astronomical system is the year n+1 B.C. (for n = 1, 2, 3, ...). Conversely, the year n B.C. is the year -(n-1) in the astronomical system. Thus year -1 = 2 B.C., year -2 = 3 B.C., and so on.

The astronomical system makes date calculations much easier. Consider the above question as to how many years elapsed between 1st January 6 B.C. and 1st January 6 A.D.? In the astronomical system this becomes: How many years elapsed between 1st January -5 and 1st January 6? The answer is: 6 - (-5) = 6 + 5 = 11 years.

Another reason for using the astronomical system of numbering years is that it makes it easier to apply the rules for leap years to years prior to 1 A.D. Most years divisible by 4 are leap years, so are the years 4 B.C., 8 B.C., and so on, leap years? No. But (using the astronomical system) years 4, 0, -4, -8, and so on, are leap years.


Suppose we choose to retain the structure of the Gregorian Calendar (with its 12 months, etc.) but to replace the system of numbering years "Anno Domini" with the astronomical system of year numbering. What implications does this have for the question of when the new millennium begins? The U.S. Naval Observatory seems to think it has none, for, although it mentions the astronomical year numbering system in the document referred to above, it continues to affirm that the new millennium begins on 1st January 2001.

A millennium is, by definition, a period of 1000 years. But it is no part of the definition that a millennium must begin or end with a particular year number. If we adopt the astronomical year numbering system then we can begin the "first" millennium with year 0 just as well as with year 1. Strictly speaking, there is no first millennium in the astronomical system, since it simply numbers years by mapping them onto the sequence ..., -2, -1, 0, 1, 2, ..., and we are free to begin millennia where we think fit. So why not divide these numbers (and the corresponding years) into segments of 1000 as follows:

-2000through-1001, 
-1000through-1, 
0through999,the "first" millennium
1000through1999,the "second" millennium
2000through2999,the "third" millennium
and so on ...

Within a millennium we may distinguish centuries as, for example:

1000through1099,the "eleventh" century
1100through1199,the "twelfth" century
...
1900through1999,the "twentieth" century
2000through2099,the "twenty-first" century
2100through2199,the "twenty-second" century
and so on ...

Within centuries we have, for example, that 1990 through 1999 is the tenth decade of the 20th century, and 2000 through 2009 is the first decade of the 21st century.

According to this convention all decades, centuries and millennia begin with a year whose number ends with "0". This applies as well to centuries and millennia preceding year 0. For example, -1000 through -901 is the first century of the millennium which precedes the first millennium (which may be called "the first pre-zero millennium").


It is thus clear that the answer to the question as to when the new millennium begins depends on which system of year-numbering one chooses to use. Christians may prefer to stay with the system of years "Anno Domini", in which case they must answer that the new millennium begins on 1st January 2001 A.D. Scientists and others who prefer a more rational and useful system of numbering years may prefer to adopt explicitly the astronomical system. In this case they are free to begin millennia from the years 1, 1001, 2001, and so on (in which case the third millennium begins on 1st January 2001), or from the years 0, 1000, 2000, and so on (in which case the third millennium begins on 1st January 2000).

Thus anyone who wishes, for whatever reason, to celebrate the start of the new millennium on 1st January 2000 has entirely good and rational grounds for doing so, namely, (i) the adoption of the astronomical system for numbering years, combined with (ii) the convention of beginning millennia with years whose numbers end in "000" (and beginning centuries with years whose numbers end in "00").

Note that this article does not show that those who hold (as those who adhere to the Christian calendar must hold) that the new millennium begins on 1st January 2001 are mistaken. Such people have reasons to justify their preference. But this article does show that anyone who prefers to think of the year 2000 as the first year of the new millennium has perfectly sound reasons for doing so, and thus for holding that:

The new millennium begins on the 1st of January in the year 2000.


Given that there will be a big celebration at the dawn of the third millennium, we might ask: What is the celebration about?

Christians, of course, answer that it is the 2000th anniversary of the birth of Christ (and might even add some apocalyptic expectations concerning the Second Coming). However, since Jesus was born in or before the year -3 (4 B.C. in the Christian calendar) the 2000th anniversary of this event (1997 at latest) has come and gone (and with no apocalypse).

Yet even those who do not adhere to the Christian dogma show a marked tendency to regard the start of the new millennium as something special. It's true that the thousands-figure in the year number does not change very often — quite seldom in history — so perhaps being alive at such a time is reason enough to celebrate.

Yet there is a deeper significance, to do with the human condition. In the long view, we divide history into centuries and millennia, especially if (as modern people tend to do) we see history as a progression from a less developed to a more developed condition. "Progress" is clear in some respects — we can travel more quickly, we can grow more food (but we cannot distribute it to all who need it), we know much more about how natural processes work and have used this knowledge to do amazing things. But whether our lives are really an improvement on the lives of people who lived a hundred, five hundred or a thousand years ago is debatable. The poverty-stricken of medieval London and Paris are matched by the poverty-stricken of modern London and Paris. The exploitation of the peasants by the feudal landlords is matched by the exploitation of modern workers by conscienceless profit-driven corporate capitalism and corrupt or incompetent governments. The spiritual aspirations of the medieval weavers are matched by those of modern office workers. But we have not stood still entirely. In the technology of mass murder we have certainly advanced far beyond what existed even a hundred years ago. And our ruthless exploitation of the natural resources of the Earth has been conducted with such efficiency that the Earth may now be preparing to rid herself of us once and for all.

Perhaps the new millennium will really see a better age, not just for a privileged elite, but for the common man and woman, and even for the animals with whom we share this planet. Perhaps we shall finally learn to throw off an outdated, obfuscating and spiritually impoverishing authority, assume responsibility for our own salvation and use our natural intelligence to create a better world for all. It is the possibility and hope of this which can give us cause for celebration on the 1st of January in the year 2000 as we enter a new era.


John R. Beattie: Millennium Start = 2000 or 2001?   A Dissenting "Either-Or" View

Kirkpatrick Sale: Five Facets of a Myth


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