The History Of Leap Year

ROME–It’s doubtful if many people during the heady days of the Roman Empire could have foreseen the economic impact that adding an extra day to the calendar every four years would create.
The Romans originally used the 355-day calendar. In order to keep up with the seasons, an extra 22 or 23-day month was added every second year or so.
Unfortunately, the Romans were not consistent in adding this extra month and by the time of Julius Cesar (circa 44 b.c.e.), the seasons, especially the vernal equinox, no longer occurred on the same calendar date–about Mar.21.
Cesar decreed that new calendars be written with an extra day every three years. He adroitly named the calendar the Julian calendar. The calendar was modified again around 8 A.D. so that they were written with an extra day every fourth year but still the calendar drifted away from the seasons.
The introduction of the Gregorian calendar in 1582 corrected the fact that the Spring Equinox was arriving 10 days earlier on the Julian calendar date of March 11th instead of March 21st, because of the uncorrected errors in the original Julian calendar. The calendar was also devised to establish a conforming date for the world’s churches to celebrate Easter.
Pope Gregory XIII of Rome refined the Julian calendar so that the number of leap years and that the average length of the civil calendar would be nearer to the natural length of the solar year. In a 400-year cycle they dropped three leap years and reduced the error from 11 minutes and 14 seconds a year to 26 seconds per year. Under this system it takes many years more for 26 seconds to accumulate into a full day. –Steve Santiago