New Year’s Day is first day of the year on the modern Gregorian calendar, as well as the Julian calendar. In pre-Christian Rome under the Julian calendar, the day was dedicated to Janus, god of gateways and beginnings, for whom January is also named.
New Year’s Day is probably the most celebrated public holiday, often observed with fireworks at the stroke of midnight as the new year starts in each time zone. Other global New Years’ Day traditions include making New Year’s resolutions and calling one’s friends and family.
Mesopotamia (Iraq) instituted the concept of celebrating the new year in 2000 BC. The first time the new year was celebrated on January 1 was in Rome in 153 BC (In fact, the month of January did not even exist until around 700 BC, when the second king of Rome 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. It was then moved back and forth, depending upon who ruled at the time.
In 1582, the Gregorian calendar reform restored January 1 as New Year’s Day. When the new calendar was put in use, the error accumulated in the 13 centuries since the Council of Nicaea was corrected by a deletion of 10 days. The Julian calendar day Thursday, 4 October 1582 was followed by the first day of the Gregorian calendar, Friday, 15 October 1582 (the cycle of weekdays was not affected). 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. Most nations of Western Europe officially adopted January 1st as New Year’s Day somewhat before they adopted the Gregorian calendar. (from me, Wikipedia and cute-calendar.com)