On the night of December 31st, as the clock strikes 12:00, we start the new year of 2018 A.D. Yet not everyone around the globe has begun celebrating the New Year. China will celebrate on February 16, while Iran on a different date, along with the entire Judaic and Islamic religions on different days as well.
January 1st and the new year are thus synonymously tied to nations influenced by Christianity. However, up until the XVIIth century, this was not the case. In 46 B.C., Caius Julius Caesar, or simply Julius Caesar, would be the first to coin January 1st as the beginning of the new year. Preceding this date, the roman calendar followed lunar cycles. A month was made up of 29 and a half days, and the new year began on March 1st. The Romans called the seventh month of the year September, the eighth, October and the ninth November. These terms, still used today, demonstrate the Roman's influence in our current calendric system.
Rome's victory against the Gallics marked a revolution in this calendric system. Unsatisfied with fluctuating months and dates, the Julius Caesar introduced a new calendar based on solar cycles. The year was to be made up of 365 days, 12 months, and four seasons to indicate the changing solar cycles. In 708, Rome adopts the solar calendar, and thus begins the "Julien calendar". However, even with their new calendric system, January 1st is not yet recognized as the new year amidst the entire region. Some celebrate on December 25, and others on March 1st. In 1564, with the edict of Rousillon, King Charles IX designates January 1st the start of the new year in all of France. In 1582, pope Gregory VIII restructures the Julien calendar and implements the Gregorian calendar which better aligns with the solar cycles, seeing as the Julien calendar had miscalculated ten solar days. The Gregorian calendar adopts January 1st as the start of the new year, following in the footsteps of Charles IX.
In 1622, the Holy-See adopts the Gregorian calendar and recognizes January 1st as the beginning of the new year in all Catholic nations. In protest, Protestants refuse to adopt the Gregorian calendar, siding with Johannes Képler who states "disagreeing with the sun is better than agreeing with the pope." However, the Gregorian calendar will continue to be adopted throughout history, with the last assimilators being the republic of China in 1949.
As a token of appreciation for the new calendric system, the Roman senate named the fifth month Quintilus in honor of Caesar. Once renamed Julius, the month takes on a new name: July. Julius' successor Auguste also contributes to altering the Julien calendar and receives his own month of Augustus, which will later become August. However, a controversy arises when Caeser's month is 31 days long, while Auguste's is only 30. To not offend either, a day is taken from February, and added to August. And this is why both July and August both have 31 days.