October 15, 1582: The Gregorian Calendar Takes Effect

The Gregorian calendar came into use on October 15, 1582, the day after October 4 in Italy, Spain, Portugal and Poland. Ten days were dropped to bring the calendar back in line with the seasons, because the old Julian calendar had been drifting by about eleven minutes a year. Pope Gregory XIII ordered the change by a bull issued in February. Protestant and Orthodox countries adopted it later, some of them centuries later.