The first time January 1 came to be considered as the beginning of the new year was back in 45 BCE. Before that, the Roman calendar began in March and consisted of 355 days. It was Roman dictator Julius Caesar who reformed the Calendar after coming to power. He instituted January 1 as the first day of the year, partly to honour the month’s namesake: Janus, the Roman god of beginnings, whose two faces allowed him to look back into the past and forward into the future.
However, it wasn’t widely accepted until the middle of the 16th century CE in Europe. With the rise of Christianity, December 25—the day of Jesus’ birth—became acceptable and January 1—the start of a new year—was recognised as heathen. It didn’t gain widespread acceptance until Pope Gregory revised the Julian calendar and declared January 1 to be the first day of a new year.
