When Was Calendar Invented. In 1582, when pope gregory xiii introduced his gregorian calendar, europe adhered to the julian calendar, first implemented by julius caesar in 46 b.c. Our modern calendar began with the julian calendar, introduced by the roman empire in 46 bc under julius caesar.
When julius caesar introduced his calendar in 45 b.c.e., he made 1 january the start of the year, and it was always the date on which the solar number and the golden number were incremented. The calendar as we know it today, is named after pope gregory xiii, who introduced it in october 1582.