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A millennium (pl. millennia) is a period of time, equal to one thousand years (from Latin mille, thousand, and annum, year). The term may implicitly refer to calendar millennia; periods tied numerically to a particular dating system, specifically ones that begin at the starting (initial reference) point of the calendar in question (typically the year 0 or the year 1) or in later years which are whole number multiples of a thousand years after it. This concept is the one primarily discussed in this article.

The term can also refer to an interval of time beginning on any date. Frequently in the latter case (and sometimes also in the former) it may have religious or theological implications (see Millenarianism). Especially in religious usage such an interval may be interpreted less precisely, being not necessarily exactly 1,000 years long.

Counting years[]


The original method of counting years was ordinal, whether 1st year A.D. or regnal 10th year of King Henry VIII. This ordinal numbering is still present in the names of the millennia and centuries, for example 1st Millennium or the 20th century, and sometimes in the names of decades, e.g. 1st decade of the 21st century.


In recent years, most people have moved to expressing individual years as cardinal numbers, for example 1945 or 1998. The usage 1999th year A.D. is no longer found. This follows scientific usage, for example astronomical year numbering. As a result, some other calendar names have also moved to cardinals, e.g. 1980s is an acceptable name for a particular decade. However, 1600s could be understood as either a decade or a century.


A change from ordinals to cardinals is incomplete and might not ever be completed; the main issues arise from the content of the various year ranges. Similar issues affect the contents of decades and centuries.

Those following ordinal year names naturally choose

  • 2001-2010 as the current decade
  • 2001-2100 as the current century
  • 2001-3000 as the current millennium

Those following cardinal year names equally naturally choose

  • 2000-2009 as the current decade
  • 2000-2099 as the current century
  • 2000-2999 as the current millennium

Debate over millennium celebrations[]

The common Western calendar, i.e. the Gregorian calendar, lacks a year numbered zero and begins instead with the year 1. For others, the year zero exists since 1582, with the changes introduced by the Papacy. Accordingly, each period of 1000 years concludes at the end of a year with three zeroes, e.g. the first thousand years in the Western calendar included the year 1000. However, there are two viewpoints about how millennia should be thought of in practice, one which relies on the formal operation of the calendar and one which appeals to other notions that attract popular sentiment.

There was a popular debate leading up to the celebrations of the year 2000 as to whether the beginning of that year should be understood (and celebrated) as the beginning of a new millennium. Historically, there has been debate around the turn of previous decades, centuries, and millennia.


As a side-note to the debate on timing of the turn of the millennium, the arbitrariness of the era itself can be raised. The Gregorian calendar is a (secular) de facto standard, based on a significant Christian event, the birth of Jesus; thus the foundation of the calendar has little or no meaning to any non-Christian celebrants. The calendar is one amongst many still in use and those used historically. Adjustments and errors in the calendar (such as Dionysius Exiguus's incorrect calculation of A.D. 1) make the particular dates we use today arbitrary.

However, given that the Gregorian calendar is an accepted standard, it is valid to discuss the significant dates within it, be it the timing of religious festivals (such as the moving date of Easter which Dionysius Exiguus was involved in calculating) or the delineation of significant periods of time, such as the end of a millennium.

Viewpoint 1: xx01-xx00[]

Those holding that the arrival of new millennium should be celebrated in the transition from 2000 to 2001 (i.e. December 31, 2000), argued that since the Gregorian Calendar has no year zero, the millennia should be counted from A.D. 1. Thus the first period of one thousand complete years runs from the beginning of A.D. 1 to the end of A.D. 1000, and the beginning of the second millennium took place at the beginning of 1001. The second millennium thus ends at the end of the year 2000. Then again, those who defend the opposite idea state that the new millennium started with the year 2000 (because of the changes made to the Gregorian calendar in 1582, or because the first millennium started in 1 A.D. and ended in 999 A.D., being the only millennium (along with the last millennium b.c.) not with 1000 years, but with 999 years).

Illustration of years with a 00-01 demarcation
2 BC 1 BC AD 1 AD 2 3 4 5 ... 998 999 1000 1001 1002 ... 1998 1999 2000 2001 2002 ... 2998 2999 3000 3001 3002
First one thousand years (millennium) Second millennium Third millennium

Arthur C. Clarke gave this analogy (from a statement received by Reuters): "If the scale on your grocer's weighing machine began at 1 instead of 0, would you be happy when he claimed he'd sold you 10 kg of tea?". This statement illustrates the common confusion about the calendar.

If one counts from the beginning of A.D. 1 to the ending of A.D. 1000, one would have counted 1000 years. The next 1000 years (millennium) would begin on the first day of 1001. In other words, the calendar is not 'cheating' anyone out of a year.

In other words, the argument is based on the fact that the last year of the first two thousand years in the Gregorian Calendar was 2000, not 1999.

Viewpoint 2: xx00-xx99[]

The "year 2000" has also been a popular phrase referring to an often utopian future, or a year when stories in such a future were set, adding to its cultural significance. There was also media and public interest in the Y2K bug. Thus, the populist argument was that the new millennium should begin when the zeroes of 2000 "rolled over", i.e. December 31 1999. People felt that the change of hundred digit in the year number, and the zeros rolling over, created a sense that a new century had begun. This is similar to the common demarcation of decades by their most significant digits, e.g. naming the period 1980 to 1989 as the 1980s or "the eighties". Similarly, it would be valid to celebrate the year 2000 as a cultural event in its own right, and name the period 2000 to 2999 as "the 2000s".

Most historians agree that Dionysius nominated Christ's birth as December 25th of the year before AD 1 (ref History Today June 1999 p60 Letters, Darian Hiles: "Of Dates and Decimals"). This corresponded with the belief that the birth year itself was considered too holy to mention. Similarly in AD 1000 the church actively discouraged any mention of that year and in modern times it labelled AD 2000 as the "Jubilee Year 2000" marking the 2000th anniversary of the birth of Christ. Year 0 has always been there, it just didn't have a name in the AD system. Thus the unnamed year 0 marked the start of the first Christian millennium, 1000 the second and 2000 the third.

Illustration of years with a 99-00 demarcation using Year zero (ISO 8601 and astronomical numbering system)
-1  0   1   2   3   4   5   ...   998   999  1000 1001 1002 ... 1998 1999 2000 2001 2002 ... 2998 2999 3000 3001 3002
First millennium (1000 years) Second millennium Third millennium
Illustration of years with a 99-00 demarcation (starting AD 1)
1 BC AD 1 2 3 4 5 ... 998 999 1000 1001 1002 ... 1998 1999 2000 2001 2002 ... 2998 2999 3000 3001 3002
0s 999 years only 1000s 2000s

Popular approach[]

The majority popular approach was to treat the end of 1999 as the end of a millennium, and to hold millennium celebrations at midnight through December 31, 1999 to January 1, 2000, as per viewpoint 2. The cultural and psychological significance of the events listed above combined to cause celebrations to be observed one year earlier than the formal Gregorian date. This does not, of course, establish that insistence on the formal Gregorian date is "incorrect", though it is widely viewed as pedantic (as in the comment of Douglas Adams mentioned below).

Some event organizers hedged their bets by calling their 1999 celebrations things like "Click" referring to the odometer like rolling over of the nines to zeros.


Stephen Jay Gould noted in his essay Dousing Diminutive Dennis' Debate (or DDDD = 2000) (Dinosaur in a Haystack) that celebrations and media announcements marked the turn into the twentieth century along the 1900-1901 border (citing, amongst other examples, the New York Times headline "Twentieth Century's Triumphant Entry"). He also included comments on adjustments to the calendar, such as those by Dionysius Exiguus (the eponymous Diminutive Dennis), the timing of celebrations over different transitional periods, and the "high" versus "pop" culture interpretation of the transition. Further of his essays on this topic are collected in Questioning the Millennium: A Rationalist's Guide to a Precisely Arbitrary Countdown.

In the editorial to 2002's Best American Essays Gould highlights the use of historical events, rather than transitional dates, to delineate periods of history: "Many commentators have stated — quite correctly in my view — that the twentieth century did not truly begin in 1900 or 1901, by any standard of historical continuity, but rather at the end of World War I, the great shatterer of illusions about progress and human betterment... I suspect that future chroniclers will date the inception of the third millennium from September 11, 2001."

(Similarly, some commentators delineate the Middle Ages from the Fall of the Western Roman Empire to the Fall of Constantinople.)

Douglas Adams highlighted the sentiment that those in favour of a 2001 celebration were pedantic spoilsports in his short web-article Significant Events of the Millennium. This sentiment was also demonstrated when, in 1997, Australian Prime Minister John Howard made a point in favour of the 2001 celebration and was named "the party pooper of the century" by local newspapers.

In an episode of the American sitcom Seinfeld entitled "The Millennium", it is revealed that the character Newman specifies the date of the millennium party that he is planning to be for the "millennium new year," meaning December 31, 2000. Thus Newman's party does not conflict with the party Kramer is planning for December 31, 1999, but will be perceived as "quite lame" according to Jerry, as the majority of people will be celebrating the new millennium on December 31, 1999.

In TV show The X-Files episode called Millennium, Scully mentions that the new millennium doesn't start until January 1, 2001. She is made fun of, but not suggested to be incorrect, when Mulder responds, "No one likes a math geek, Scully."

Jeopardy! game show host Alex Trebek proudly welcomed his guests and contestants to the "first day of the twenty-first century" on the January 1, 2001 episode.

Millennium is also the name of a popular show by Chris Carter (The X-Files) starring Lance Henriksen as a retired F.B.I. agent working for the "Millennium Group" a criminal consulting firm, during the approach of the year 2000. This nearing of the Millennium seemed to cause a rise in crime and possible supernatural events. This television show lived through three seasons and a seventh season episode of The X-Files. It was known as the darkest show on television.

Although popular culture generally observed the start of the 21st century and 3rd millennium on January 1, 2000, the start of the 20th century was generally observed on January 1 1901 (newspapers dated January 1 1900 generally make little mention of the change of digit).


Millenium (pl. millenia) is a common misspelling of millennium (pl. millennia), found in many advertisements near the end of 1999.

See also[]

External links[]