The Gregorian Calendar was adopted for the first time on October 15, 1582.

Use of the new calendar was decreed by by Pope Gregory XIII when he issued the papal bull Inter gravissimas.

425 Years of Gregorian Calendar
Issued by Montenegro in 2007
Designed by Jadranka Simonović

 

The Gregorian calendar was introduced by Pope Gregory XIII in 1582, in response to the drift of the equinoxes, which was affecting the determination of the date of Easter.

The Julian calendar’s method of leap years was too simplistic, causing the calendar to gain about three days every four centuries relative to the equinoxes.

The Gregorian reform omitted 10 days from the calendar to realign it with the equinoxes and modified the leap year algorithm.

In the Gregorian calendar, a year is a leap year if it is divisible by 4, except for end-of-century years, which must be divisible by 400. This change reduced the calendar year from an average of 365.25 days to 365.2425 days, aligning it more closely with the solar year of approximately 365.2422 days.
Difference between Julian Calendar and Gregorian Calendar – World History Edu

 

Last year marked the anniversary of Napoleon’s final exile to St. Helena.