The Pedant's Millennium

Updated August 5, 2020 | Infoplease Staff

When Does the Millennium Officially Begin?

Although January 1, 2000, was celebrated throughout the world as the start of the new millennium, that honor should have technically been reserved for January 1, 2001. Common sense might suggest that the year 2000 was the dawning of the third millennium, but it was in fact the waning of the second.

The first millennium began in A.D. 1.

There is no year zero in our calendar: the sequence of years passes directly from 1 B.C. to A.D. 1. Adding a thousand years to the year 1 equals the year 1001, marking the start of the second millennium. Add another thousand to reach the beginning of the third millennium: January 1, 2001. Opinion seems to be divided about whether the insistence on 2001 is overbearingly pedantic or simply sticking to the facts.

A Fundamental Calendrical Flaw

Bear in mind, however, that both 2000 and 2001 are years based on a fundamental calendrical flaw. The 6th-century monk Dionysius Exiguus (also called Dennis the Short) recast the calendar so that years would be counted from the birth of Christ (anno Domini [A.D.]; in the year of the Lord) instead of the beginning of the reign of the Roman emperor Diocletian (anno Diocletiani). A.D. 532–formerly anno Diocletiani 248–became the first year counted according to the Christian era. Dionysius, however, miscalculated the birth of Christ, which is believed by many scholars to have been 4 B.C.

Had the years been recalibrated accordingly, the millennium would have occurred on Jan. 1, 1997. In other words, why squabble about the millennium—we've already missed it!