The earliest recorded festivities in honor of a new year's arrival date back some 4,000 years to ancient Babylon. For the Babylonians, the first new moon following the vernal equinox—the day in late March with an equal amount of sunlight and darkness—heralded the start of a new year.

When was new year's first celebrated?

In 45 B.C., New Year's Day is celebrated on January 1 for the first time in history as the Julian calendar takes effect. Soon after becoming Roman dictator, Julius Caesar decided that the traditional Roman calendar was in dire need of reform.

How did January 1 become the new year?

Julius Caesar thought it would be appropriate for January, Janus's namesake month, to be the doorway to a new year, and when he created the Julian calendar, he made January 1 the first day of the year (this also put the calendar year in line with the consular year, as new consuls also took office that day).