We can partly thank the Roman king Numa Pompilius. According to tradition, during his reign (c. 715–673 BCE) Numa revised the Roman republican calendar so that January replaced March as the first month. It was a fitting choice, since January was named after Janus, the Roman god of all beginnings; March celebrated Mars, the god of war. (Some sources claim that Numa also created the month of January.) However, there is evidence that January 1 was not made the official start of the Roman year until 153 BCE.

In 46 BCE Julius Caesar introduced more changes, though the Julian calendar, as it became known, retained January 1 as the year’s opening date. With the expansion of the Roman Empire, the use of the Julian calendar also spread. However, following the fall of Rome in the 5th century CE, many Christian countries altered the calendar so that it was more reflective of their religion, and March 25 (the Feast of the Annunciation) and December 25 (Christmas) became common New Year’s Days.

It later became clear that the Julian calendar required additional changes due to a miscalculation concerning leap years. The cumulative effect of this error over the course of several centuries caused various events to take place in the wrong season. It also created problems when determining the date of Easter. Thus, Pope Gregory XIII introduced a revised calendar in 1582. In addition to solving the issue with leap years, the Gregorian calendar restored January 1 as the start of the New Year. While Italy, France, and Spain were among the countries that immediately accepted the new calendar, Protestant and Orthodox nations were slow to adopt it. Great Britain and its American colonies did not begin following the Gregorian calendar until 1752. Before then they celebrated New Year’s Day on March 25.

Over time non-Christian countries also began to use the Gregorian calendar. China (1912) is a notable example, though it continued to celebrate the Chinese New Year according to a lunar calendar. In fact, many countries that follow the Gregorian calendar also have other traditional or religious calendars. Some nations never adopted the Gregorian calendar and thus start the year on dates other than January 1. Ethiopia, for example, celebrates its New Year (known as Enkutatash) in September.

Read the original article on britannica.com.

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