JULIAN CALENDAR - The Julian Calendar was introduced in 46 BC by Julius Caesar and took force in 45 BC (709 ab urbe condita). It was developed in consultation with the Alexandrian astronomer Sosigenes and was probably designed to approximate the tropical year. It has a regular year of 365 days divided into 12 months, and a leap day is added to February every four years. Hence, the Julian Calendar's year is on average 365¼ days long.
The Julian Calendar remained in use into the 20th century in some countries, particularly in eastern Europe, and is still used by the majority of Orthodox faithful for ecclesiastical dates.