January Joins the Calendar
The first time the new year was celebrated on January 1st was in Rome in 153 B.C. (In fact, the month of January did not even exist until around 700 B.C., when the second king of Rome, Numa Pontilius, added the months of January and February.) The new year was moved from March to January because that was the beginning of the civil year, the month that the two newly elected Roman consuls—the highest officials in the Roman republic—began their one-year tenure. But this new year date was not always strictly and widely observed, and the new year was still sometimes celebrated on March 1.
Julian Calendar: January 1st Officially Instituted as the New Year
In 46 B.C. Julius Caesar introduced a new, solar-based calendar that was a vast improvement on the ancient Roman calendar, which was a lunar system that had become wildly inaccurate over the years. The Julian calendar decreed that the new year would occur with January 1, and within the Roman world, January 1 became the consistently observed start of the new year.
Middle Ages: January 1st Abolished
In medieval Europe, however, the celebrations accompanying the new year were considered pagan and unchristian like, and in 567 the Council of Tours abolished January 1 as the beginning of the year. At various times and in various places throughout medieval Christian Europe, the new year was celebrated on Dec. 25, the birth of Jesus; March 1; March 25, the Feast of the Annunciation; and Easter.
Gregorian Calendar: January 1st Restored
In 1582, the Gregorian calendar reform restored January 1 as new year's day. Although most Catholic countries adopted the Gregorian calendar almost immediately, it was only gradually adopted among Protestant countries. The British, for example, did not adopt the reformed calendar until 1752. Until then, the British Empire —and their American colonies— still celebrated the new year in March.