In 46 B.C.E. the Roman emperor Julius Caesar first established January 1 as New Year’s Day. Janus was the Roman god of doors and gates, and had two faces, one looking forward and one back. Caesar felt that the month named after this god (“January”) would be the appropriate “door” to the year. Caesar celebrated the first January 1 New Year by ordering the violent routing of revolutionary Jewish forces in the Galilee. Eyewitnesses say blood flowed in the streets. In later years, Roman pagans observed the New Year by engaging in drunken orgies—a ritual they believed constituted a personal re-enacting of the chaotic world that existed before the cosmos was ordered by the gods.
As Christianity spread, pagan holidays were either incorporated into the Christian calendar or abandoned altogether. By the early medieval period most of Christian Europe regarded Annunciation Day (March 25) as the beginning of the year. (According to Catholic tradition, Annunciation Day commemorates the angel Gabriel’s announcement to Mary that she would be impregnated by G-d and conceive a son to be called Jesus.)
After William the Conqueror (AKA “William the Bastard” and “William of Normandy”) became King of England on December 25, 1066, he decreed that the English return to the date established by the Roman pagans, January 1. This move ensured that the commemoration of Jesus’ birthday (December 25) would align with William’s coronation, and the commemoration of Jesus’ circumcision (January 1) would start the new year - thus rooting the English and Christian calendars and his own Coronation). William’s innovation was eventually rejected, and England rejoined the rest of the Christian world and returned to celebrating New Year's Day on March 25.
About five hundred years later, in 1582, Pope Gregory XIII (AKA “Ugo Boncompagni”, 1502-1585) abandoned the traditional Julian calendar. By the Julian reckoning, the solar year comprised 365.25 days, and the intercalation of a “leap day” every four years was intended to maintain correspondence between the calendar and the seasons. Really, however there was a slight inaccuracy in the Julian measurement (the solar year is actually 365 days, 5 hours, 48 minutes and 46 seconds = 365.2422 days). This slight inaccuracy caused the Julian calendar to slip behind the seasons about one day per century. Although this regression had amounted to 14 days by Pope Gregory’s time, he based his reform on restoration of the vernal equinox, then falling on March 11, to the date had 1,257 years earlier when Council of Nicaea was convened (March 21, 325 C.E.). Pope Gregory made the correction by advancing the calendar 10 days. The change was made the day after October 4, 1582, and that following day was established as October 15, 1582. The Gregorian calendar differs from the Julian in three ways: (1) No century year is a leap year unless it is exactly divisible by 400 (e.g., 1600, 2000, etc.); (2) Years divisible by 4000 are common (not leap) years; and (3) once again the New Year would begin with the date set by the early pagans, the first day of the month of Janus - January 1.
On New Year's Day 1577 Pope Gregory XIII decreed that all Roman Jews, under pain of death, must listen attentively to the compulsory Catholic conversion sermon given in Roman synagogues after Friday night services. On New Year's Day 1578 Gregory signed into law a tax forcing Jews to pay for the support of a “House of Conversion” to convert Jews to Christianity. On New Year's 1581 Gregory ordered his troops to confiscate all sacred literature from the Roman Jewish community. Thousands of Jews were murdered in the campaign.
Throughout the medieval and post-medieval periods, January 1 - supposedly the day on which Jesus’ circumcision initiated the reign of Christianity and the death of Judaism - was reserved for anti-Jewish activities: synagogue and book burnings, public tortures, and simple murder.
The Israeli term for New Year’s night celebrations, “Sylvester,” was the name of the “Saint” and Roman Pope who reigned during the Council of Nicaea (325 C.E.). The year before the Council of Nicaea convened, Sylvester convinced Constantine to prohibit Jews from living in Jerusalem. At the Council of Nicaea, Sylvester arranged for the passage of a host of viciously anti-Semitic legislation. All Catholic “Saints” are awarded a day on which Christians celebrate and pay tribute to that Saint’s memory. December 31 is Saint Sylvester Day - hence celebrations on the night of December 31 are dedicated to Sylvester’s memory.
U.S. News and World Report December 23, 1996