When Did the Concept of the Leap Year Originate?

When did the actual concept of the leap year originate?

In 1582, on February 24th, was decided that the day after 'Thursday, October 4th, 1582' would be 'Friday, October 15th, 1582'. Details below...

In 1582, Pope Gregory XIII (13th), January 7th, 1502 - April 10th, 1585, Pope of the Catholic Church from May 13th, 1572 to his death in 1585, commissioned the adjustment of the Julian calendar, that was in use at that time, and which was already generating significant discrepancies over the astronomical year.

The new calendar was instituted when Pope Gregory decreed, by the papal bull Inter gravissimas of February 24th, 1582, that the day after Thursday, October 4th, 1582 would be not Friday, October 5th, but Friday, October 15th, 1582.

Articles on the leap years

1. What is a leap year? What is a common year?

2. How often do the leap years occur in the calendar?

3. Why do we need leap years?

4. Leap years algorithm. Examples.

5. When did the actual concept of the leap year originate?

6. The modern (Gregorian) calendar and the Julian one. Julian calendar adjustment

7. How accurate is the Gregorian calendar, based on the leap year algorithm?

List of all the leap years between 1582 and 4818.

Leap years calculator. Is it a leap year or a common one?