When Was Gregorian Calendar Adopted. Pope gregory xiii introduced the gregorian calendar in 1582 via a papal bull, because the julian calendar was becoming inaccurate, especially in the calculation of the date. Most cultures in the ancient near east relied on a calendar in which months had alternating lengths of 29 and 30 days and added a month about every third year.

On september 14, 1752, great britain and its colonies experienced an unusual calendar shift that altered the daily lives of its residents. Adopted by act of parliament (stat.