Historedia
EuropeEvent

Implementation of the Gregorian Calendar by Pope Gregory XIII

When
1582
Where
Papal States
Episodes
1

Pope Gregory XIII issued the papal bull Inter gravissimas on 24 February 1582, instituting the Gregorian calendar. The reform mandated that Thursday, 4 October 1582, be followed immediately by Friday, 15 October 1582, correcting the Julian calendar's drift.

Episodes

  1. 24 February 1582 · Papal StatesIssuance of Inter gravissimas

    Pope Gregory XIII issued the papal bull Inter gravissimas on 24 February 1582, formally instituting the Gregorian calendar as a replacement for the Julian calendar.

Background and detail

The Decree. On 24 February 1582, Gregory XIII issued the papal bull Inter gravissimas. This document formally introduced the new calendar as a modification of the Julian system, establishing the legal framework for the date adjustment within the Catholic Church and Papal States.

Implementation. The reform advanced the date by ten days. Consequently, the Julian calendar day Thursday, 4 October 1582, was followed directly by the first day of the Gregorian calendar, Friday, 15 October 1582, without affecting the cycle of weekdays.

People involved

Sources

  1. Pope Gregory XIII Wikipedia, revision of 2026-07-11
  2. Gregorian calendar Wikipedia, revision of 2026-09-11

Machine-drafted from the cited Wikipedia passages and checked by a reviewing model, not by a human editor. Every passage cites the revision it was written from; dates and places follow those passages.