Origin Of Gregorian Calendar. Let’s learn what the gregorian calendar is, how it became the most common calendar, which countries use or don't use it, and what happened during the years of “double. Officially introduced by pope gregory xiii in october 1582, the calendar was.

The gregorian calendar came into force on the day after october 4, 1582, by virtue of a papal bull that ordered it. Let’s learn what the gregorian calendar is, how it became the most common calendar, which countries use or don’t use it, and what happened during the years of “double.