January is named for Janus (Ianuarius), the god of the doorway; the name has its beginnings in Roman mythology, coming from the Latin word for door (ianua) - January is the door to the year. Traditionally, the original Roman calendar consisted of 10 months, totalling 304 days, winter being considered a monthless period. Around 713 BC, the semi-mythical successor of Romulus, King Numa Pompilius, is supposed to have added the months of January and February, allowing the calendar to equal a standard lunar year (355 days). Although March was originally the first month in the old Roman Calendar, January became the first month of the calendar year either under Numa or under the Decemvirs about 450 BC (Roman writers differ). In contrast, years in dates were identified by naming two consuls, who entered office on May 1 and March 15 before 153 BC when they began to enter office on January 1.
Various Christian feast dates were used for the New Year in Europe during the Middle Ages, including March 25 and December 25. However, medieval calendars were still displayed in the Roman fashion of twelve columns from January to December. Beginning in the 16th century, European countries began officially making January 1 the start of the New Year once again — sometimes called Circumcision Style because this was the date of the Feast of the Circumcision, being the 8th day from December 25.
Historical names for January include its original Roman designation, Ianuarius, the Saxon term Wulf-monath (meaning wolf month) and Charlemagne's designation Wintarmanoth (winter / cold month). In Finnish, the month is called tammikuu, meaning month of the oak, but the original meaning was the month of the heart of winter, as tammi has initially meant axis or core. This month is in Czech called leden, meaning ice month.
New Year's Day is the first day of the new year. On the modern Gregorian calendar, it is celebrated on January 1, as it was also in ancient Rome (though other dates were also used in Rome). In all countries using the Gregorian calendar, except for Israel, it is a public holiday, often celebrated with fireworks at the stroke of midnight as the new year starts. January 1 on the Julian calendar corresponds to January 14 on the Gregorian calendar, and it is on that date that followers of some of the Eastern Orthodox churches celebrate the New Year.