The Julian calendar was introduced by Julius Caesar in 45 BCE as a reform of the Roman calendar. It was in use throughout the Roman Empire and later the Byzantine Empire, until it was replaced by the Gregorian calendar in most countries in the 16th and 17th centuries.
The Julian calendar has a regular year of 365 days divided into 12 months, with a leap year of 366 days every four years. The leap year is added February.
The Julian calendar was used in many parts of the world, including Europe, the Americas, and parts of Africa and Asia, for centuries, and it is still used in some communities today.