January 1: The Julian calendar took effect for the first time (45 BC)

Julius Caesar

The Julian calendar took effect for the first time. It was the basis of the Gregorian calendar, which is the current western calendar and internationally accepted civil calendar. The Julian calendar was a reform of the Roman calendar by Julius Caesar, which has a regular year of 365 days divided into 12 months with a leap day added to February every four years. It was very close to the modern calendar, however, its solar year has 11 minutes more than the actual year. To be precise, the Gregorian calendar replaced the Julian calendar in 1582.