The first time January 1 came to be considered the beginning of the new year was back in 45 BCE. The Roman calendar before that began in March and consisted of 355 days. An additional 27-day or 28-day intercalary month would sometimes be inserted between February and March.
Roman dictator Julius Caesar reformed the calendar soon after coming to power in the late first century BCE. But even as the Julian calendar gained popularity, large parts of Europe did not accept it till well into the mid-16th century CE. With the advent of Christianity, January 1 as the beginning of a new year was seen as pagan, while December 25, with its religious connotations regarding the birth of Jesus, was considered more acceptable.
There was also the issue of misplaced calculation on the part of Caesar, due to which the new year day often kept shifting. After Pope Gregory reformed the Julian calendar and standardized January 1 as the first day of a new year, it slowly acquired currency across the world.
The calendar made by Julius Caesar
The early Roman calendar was conceived by Romulus, the founder of Rome, in the 8th century BCE. Numa Pompilius, who came to power a year later, made it a 12-month year by adding the months of Januarius and Februarius.
But this calendar, which followed the lunar cycle, frequently fell out of sync with the seasons. Moreover, the pontifices, or the member of the council of priests assigned to oversee the calendar, were often accused of adding days to interfere with election dates or extend a political term.
After Julius Caesar came to power in 46 BCE, he attempted to reform the calendar, for which he took the advice of Alexandrian astronomer, Sosigenus. Sosigenus suggested doing away with the lunar cycle and following the sun instead, the way the Egyptians did. Accordingly, the year was calculated at 365 and ¼ days.
Interestingly, Caesar added 67 days to the year 46 BCE so that the new year in 45 BCE could begin on January 1. The date was chosen to honor the Roman God of beginnings, Janus, who is believed to have two faces- one looking back into the past and the other to the future. After that, ancient Romans celebrated the day by offering sacrifices to Janus and exchanging gifts with one another.
However, with the spread of Christianity, the celebration of a Roman God was seen as a pagan ritual in many parts of Europe. Accordingly, Christian leaders attempted to celebrate the beginning of a new year on a day with more religious significance in medieval Europe, like December 25 (Christmas) or March 25 (the feast of Annunciation).
Caesar and Sosigenus also made an error in calculating the number of days in a solar year. The actual number of days in a solar calendar is 365.24199 instead of the 365.25 that Caesar had calculated. Consequently, there was a gap of 11-minutes every year, which added up to about 11 days by the year 1582. “This defect was of principle concern to the pope; if the Julian calendar had continued in service, Easter would eventually have been celebrated in the summer,” writes historian Gordon Moyer, in his article, ‘The Gregorian calendar after that began the effort to standardize a calendar most suitable to the Christian life of the middle ages.
The calendar made by Pope Gregory XIII
The reform was not easy. Pope Gregory assembled an eminent body of astronomers, mathematicians, and clergymen for the purpose. The main challenge it faced was afflicting almost every civil calendar, dealing with a fraction of dangling at the end of the year.
In order to fix the miscalculation of the Julian calendar, Aloysius Lilius, the Italian scientist who worked on the Gregorian calendar, devised a new system whereby every fourth year would be a leap year, but century years that were not divisible by 400 were exempted. For instance, 1600 and 2000 were leap years, but not 1700, 1800, and 1900. These revisions were formally instituted by the papal bull of February 24, 1582, setting off a furious debate among religious leaders and scholars.
The religious opposition to the reform was, in essence, against Catholicism. “This was the age of Reformation; Protestant countries rejected the new calendar, denouncing it as a papal scheme to bring their rebellious fold back under the jurisdiction of Rome,” writes Moyer. He adds that the accusation was not entirely unfounded since Gregory XIII was a ruthless promoter of counter-Reformation.
Consequently, the Catholic countries like Italy, Spain, and Portugal were quick to adopt the new system. Protestant countries like England and Germany held off till about the end of the 18th century. Some accounts suggest that a riot took place in the streets of England in the year 1752 when the country went on to adopt the new calendar. The last European country to adopt the Gregorian calendar was Greece in 1923.
While the European colonies in the Americas adopted the new calendar when their mother countries did, large parts of the non-European world too began adopting it over the 20th century. Japan, for instance, replaced its traditional lunisolar calendar with the Gregorian one in 1872, while China adopted it in 1912.
There are some countries, including India, Bangladesh, Pakistan, Mynamar, Israel, where the traditional calendar is used alongside the Gregorian one. In India, the Saka calendar, which begins with the Chaitra month (March 21/22), is used along with the Gregorian calendar for most official purposes.