On May 13, 1572 he was crowned [[Pope]] Gregorius XIII. On October 5, 1582, he introduced the [[Gregorian Calendar]], the calendar which is used today. The previous [[Julian Calendar]] ran ten days behind, and to compensate, the date moved to October 15 after October 4. | On May 13, 1572 he was crowned [[Pope]] Gregorius XIII. On October 5, 1582, he introduced the [[Gregorian Calendar]], the calendar which is used today. The previous [[Julian Calendar]] ran ten days behind, and to compensate, the date moved to October 15 after October 4. |