New Year's Eve occurs on the eve of December 31st, and when the clock strikes midnight, we celebrate the start of a fresh new calendar year that starts on January 1st. But it wasn't always like this; the first month of the year was invented by the ancient Romans. Here's how the calendar became what it is today.
Before the modern calendar was created, there were various ways that people around the world tracked time: Ancient Egyptians used the sun, while Mesolithic people of Britain relied on the moon's different phases. Until the Romans started working on their first calendar in 509 B.C. Throughout the Roman Republic, the calendar shifted many times. The first one was constructed using only ten months, which started in March and ended in December when the harvest was over. The year lasted 304 days; 6 months included 30 days, while the remaining 4 had 31 days. March, April, May, and June were named after Roman gods. For example, March was the God of Mars, Martius, and June was Juno, goddess of childbirth. The following six were based on the first 6 Latin letters; September comes from Septem, meaning 7.
After their first attempt, the Romans' next interpretation of time was the Lunar calendar. It was developed when the second king Numa Pompilius was in charge around the seventh century BC. Since Romans thought odd numbers were propitious, they wanted every month to have an odd number of days. To do so, they included two new 28-day months, Ianuarius, named after the god Janus, and Februarius, for Februa, a Roman purification festival. This was only possible after removing one day from every month of the former calendar and adding an extra 50 days to the whole year. February was the last month, and it was the only one with even numbers, so it was known as unlucky. The revised calendar eventually failed because it was based on the phases of the moon that lasted 29.5 days, meaning the seasons didn't match up with the months the way they had expected.
At last, in 45 B.C., the Julian calendar, named after Julius Caesar, was produced. The 365-day year was suggested by Sosigenes of Alexandria. The astronomer and mathematician based the months off the sun. He also said that there would be a leap year in February every four years, and the new year would start on January 1st. Unfortunately, not many people honored the new celebration date. It wasn't until 1582, when the Gregorian calendar was formed, that people truly accepted the new year's date that most of the world still uses. The Julius 365.25 days year was changed to 365.2425 days to fit the sun's changes better.
And while the Gregorian calendar is the leading one used today, some cultures and religions follow different timetables for celebration, such as Chinese New Year and Jewish New Year, Rosh Hashana.