Leap Year Julian Calendar. It was developed in consultation with the Alexandrian astronomer Sosigenes and was probably designed to approximate the tropical year. This method of adding a "leap day" every fourth year averaged out to.
The following chart shows what month the DDD part of a Julian date represents in leap years. A tropical year factors in the actual time it takes the planet Earth to complete a full revolution around the sun. The Julian calendar's formula to calculate leap years produced a leap year every four years.
This new "Julian" calendar was used throughout the Roman Empire and by various Christian churches.
In Julius's calendar the rule for leap years was that every third year shall be a leap year.
Eleven minutes doesn't sound like much. This method of adding a "leap day" every fourth year averaged out to. It was developed in consultation with the Alexandrian astronomer Sosigenes and was probably designed to approximate the tropical year.