Many years ago, the Romans had a god named Janus. He was the master of doors and gates, and he had two faces - one that looked forward and one who looked back. Julius Caesar thought it would be appropriate for January, the month appointed after Janus, to be a door to a new year, and when he created the Julian calendar, he did January 1 the first day of the year.
For Caesar, the Julian calendar was a political gadget and a weapon. As the Roman armies invaded new lands, the Empire often allowed the subordinate nations to preserve social and religious habits. After the creation of the calendar, it was decided to use it in every corner of the Empire, not merely for the sake of consistency, but to remind all the citizens about Roman authority and the power of Caesar.
After Rome fell and the Reformation spread to Europe, the New Year celebration was seen as a pagan ritual, so the first day of the year moved to a more appropriate date for Christianity. Some states started the year on March 25, the day when Christians celebrate Mary's pregnancy. Other states used the day of Christmas, December 25, while others used on Easter Sunday, regardless of the date on which it fell. Often, this change is reflected only in the government calendar. In everyday life, January 1 remained the first day of the year, as ordinary people, who did not belong to the rogue or royal families, did not see any reason to change it.
Chaos on calendars worked for some time, but a pope who came to the top of the nose mess at the end of the Middle Ages. An error in Caesar's calendar caused Julian's year to fall wrongly in line with the solar year. In 1582, the difference reached 10 years. Over time, Spring Equinox (and consequently, Easter) went on date, and Pope Gregory XIII was tired of restoring the feast. Gregory created a new calendar that used an extra day at the end of February every four years to stay regular. He also finally decided January 1 as the first day of the year.
Most Catholic countries quickly adopted the Gregorian calendar, but the Protestant and eastern rite states hesitated a bit. Protestants complained that the "Roman Antichrist" was trying to deceive, to worship the wrong days. The Rites of the East Rite followed the Julian calendar for several centuries, while Russia adopted the Gregorian calendar after the 1917 revolution. To this day, the Eastern Orthodox Church follows either the traditional Julian calendar or edited to organize the liturgical year.
Over time, Protestant nations began using the Gregorian calendar. Most of us, changed the start of the year long before they adopted the whole calendar. England, Ireland, and British colonies made January 1 beginning of the year in early 1753 - Scotland had made this change 150 times before, but waited until September to fully embrace the new calendar. The delayed movement was more likely, symbolically, after joining the government calendar with that of the people before joining the government calendar with that of the Pope.
Source: Mental Flos
