Mesopotamia (Iraq) instituted the concept of celebrating the new year in 2000 BC and celebrated new year around the time of the vernal equinox, in mid-March. The early Roman calendar designated March 1 as the new year. The calendar had just ten months, beginning with March. That the new year once began with the month of March is still reflected in some of the names of the months. September through December, our ninth through twelfth months, were originally positioned as the seventh through tenth months. (Septem is Latin for "seven"; octo, "eight"; novem, "nine"; and decem, "ten".) Roman legend usually credited their second king Numa with the establishment of the months of January and February. These were first placed at the end of the year, but at some point came to be considered the first two months instead.
The January Kalends (Latin: Kalendae Ianuariae) came to be celebrated as the new year at some point after it became the day for the inaugurating new consuls in 153 BC. Romans had long dated their years by these consulships, rather than sequentially, and making the kalends of January start the new year aligned this dating. Still, private and religious celebrations around the March new year continued for some time and there is no consensus on the question of the timing for January 1's new status. Once it became the new year, however, it became a time for family gatherings and celebrations. A series of disasters, notably including the failed rebellion of M. Aemilius Lepidus in 78 BC, established a superstition against allowing Rome's market days to fall on the kalends of January and the pontiffs employed intercalation to avoid its occurrence.
In AD 567, the Council of Tours formally 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 December 25 in honor of the birth of Jesus; March 1 in the old Roman style; March 25 in honor of Lady Day and the Feast of the Annunciation; and on the movable feast of Easter. These days were also astronomically and astrologically significant since, at the time of the Julian reform, March 25 had been understood as the spring equinox and December 25 as the winter solstice. (The Julian calendar's small disagreement with the solar year, however, shifted these days earlier before the Council of Nicaea which formed the basis of the calculations used during the Gregorian reform of the calendar.) Medieval calendars nonetheless often continued to display the months running from January to December, despite their readers reckoning the transition from one year to the next on a different day.
Among the 7th century pagans of Flanders and the Netherlands, it was the custom to exchange gifts on the first day of the new year. This custom was deplored by Saint Eligius (died 659 or 660), who warned the Flemish and Dutch: "(Do not) make vetulas, [little figures of the Old Woman], little deer or iotticos or set tables [for the house-elf, compare Puck] at night or exchange New Year gifts or supply superfluous drinks [another Yule custom]." However, on the date that European Christians celebrated the New Year, they exchanged Christmas presents because New Year's Day fell within the twelve days of the Christmas season in the Western Christian liturgical calendar; the custom of exchanging Christmas gifts in a Christian context is traced back to the Biblical Magi who gave gifts to the Child Jesus.
Because of the leap year error in the Julian calendar, the date of Easter had drifted backward since the First Council of Nicaea decided the computation of the date of Easter in 325. By the sixteenth century, the drift from the observed equinox had become unacceptable. In 1582, Pope Gregory XIII declared the Gregorian calendar widely used today, correcting the error by a deletion of 10 days. The Gregorian calendar reform also (in effect) 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 its American colonies – still celebrated the new year on 25 March.
Most nations of Western Europe officially adopted 1 January as New Year's Day somewhat before they adopted the Gregorian Calendar. In Tudor England, New Year's Day, along with Christmas Day and Twelfth Night, was celebrated as one of three main festivities among the twelve days of Christmastide. There, until the adoption of the Gregorian Calendar in 1752, the first day of the new year was the Western Christian Feast of the Annunciation, on 25 March, also called "Lady Day". Dates predicated on the year beginning on 25 March became known as Annunciation Style dates, while dates of the Gregorian Calendar commencing on 1 January were distinguished as Circumcision Style dates, because this was the date of the Feast of the Circumcision, the observed memorial of the eighth day of Jesus Christ's life after his birth, counted from the latter's observation on Christmas, 25 December. Pope Gregory acknowledged 1 January as the beginning of the new year according to his reform of the Catholic Liturgical Calendar.