Inter gravissimas
Inter gravissimas was a papal bull
Papal bull
A Papal bull is a particular type of letters patent or charter issued by a Pope of the Catholic Church. It is named after the bulla that was appended to the end in order to authenticate it....

 issued by Pope Gregory XIII
Pope Gregory XIII
Pope Gregory XIII , born Ugo Boncompagni, was Pope from 1572 to 1585. He is best known for commissioning and being the namesake for the Gregorian calendar, which remains the internationally-accepted civil calendar to this date.-Youth:He was born the son of Cristoforo Boncompagni and wife Angela...

 on February 24, 1582. The document reformed the Julian calendar
Julian calendar
The Julian calendar began in 45 BC as a reform of the Roman calendar by Julius Caesar. It was chosen after consultation with the astronomer Sosigenes of Alexandria and was probably designed to approximate the tropical year .The Julian calendar has a regular year of 365 days divided into 12 months...

 and created a new calendar which came to be called the Gregorian calendar
Gregorian calendar
The Gregorian calendar, also known as the Western calendar, or Christian calendar, is the internationally accepted civil calendar. It was introduced by Pope Gregory XIII, after whom the calendar was named, by a decree signed on 24 February 1582, a papal bull known by its opening words Inter...

, which is used in most countries today.


The intention expressed by the text of this bull was "to restore" the calendar so that seasonal events critical for the calculation of Easter dates would be back in their "proper places" and would be prevented from being moved away again. The idea of reform as such is not otherwise mentioned. The bull identifies "three necessary" things for the correct determination of Easter dates: correct placement of the northern vernal equinox; correct identification of the "14th day of the moon" (effectively full moon) that happens on or next after the vernal equinox, and the first Sunday that follows that full moon. The first two items were the ones that received attention; the third, about choosing the next following Sunday, was not identified as causing any problem, and was not further mentioned.

By "restore", Gregory meant two things. First, he adjusted the calendar so that the vernal equinox was near March 21, where it had been during the Council of Nicaea (May 20 – August 25, 325). This required removing ten days of drift. Second, he made the tabular 14th day of the moon correspond with the real full moon, removing "four days and more" of drift. This would restore the dates of Easter to near where they were at the time of the Council of Nicaea, although that council had not specified where in the calendar the vernal equinox should fall, and had not adopted any particular type of lunar tables. The practices of the Roman Catholic Church
Roman Catholic Church
The Catholic Church, also known as the Roman Catholic Church, is the world's largest Christian church, with over a billion members. Led by the Pope, it defines its mission as spreading the gospel of Jesus Christ, administering the sacraments and exercising charity...

 that had become traditional by 1582 for calculating the Easter and lunar calendars became settled when Dionysius Exiguus
Dionysius Exiguus
Dionysius Exiguus was a 6th-century monk born in Scythia Minor, modern Dobruja shared by Romania and Bulgaria. He was a member of the Scythian monks community concentrated in Tomis, the major city of Scythia Minor...

 translated the rules of the Church of Alexandria
Church of Alexandria
The Church of Alexandria in Egypt is the particular church headed by the Patriarch of Alexandria. It is one of the original four Apostolic Sees of Christianity, with Rome, Antioch and Jerusalem ....

 from Greek
Greek language
Greek is an independent branch of the Indo-European family of languages. Native to the southern Balkans, it has the longest documented history of any Indo-European language, spanning 34 centuries of written records. Its writing system has been the Greek alphabet for the majority of its history;...

 into Latin
Latin is an Italic language originally spoken in Latium and Ancient Rome. It, along with most European languages, is a descendant of the ancient Proto-Indo-European language. Although it is considered a dead language, a number of scholars and members of the Christian clergy speak it fluently, and...

 in 525. (Britain adopted them at the Council of Whitby in 664 and France adopted them about 775. Before these years, France and Rome used the tables of Victorius of Aquitaine
Victorius of Aquitaine
Victorius of Aquitaine, a countryman of Prosper of Aquitaine and also working in Rome, produced in 457 an Easter Cycle, which was based on the consular list provided by Prosper's Chronicle. This dependency caused scholars to think that Prosper had been working on his own Easter Annals for quite...

, which were published in 457. Britain before 664 and Rome before 457 used an 84-year Paschal cycle.)

Gregory also made changes to the calendar rules, intending to ensure that, in the future, the equinox and the 14th day of the Paschal moon, and consequently Easter Sunday, would not move away again from what the bull called their proper places.

The changes (relative to the Julian calendar) were as follows:

1. reduction of the number of leap year
Leap year
A leap year is a year containing one extra day in order to keep the calendar year synchronized with the astronomical or seasonal year...

s - centennial years, such as 1700, 1800, and 1900 ceased to be leap years, but years that can be divided by 400, such as 1600 and 2000 continued to be;

2. turning back extra days - October 4, 1582, was to be followed by October 15, 1582, and these 10 missing days were not to be counted in calculating end days of loans, etc.;

3. Easter
Easter is the central feast in the Christian liturgical year. According to the Canonical gospels, Jesus rose from the dead on the third day after his crucifixion. His resurrection is celebrated on Easter Day or Easter Sunday...

 was to be computed with reference not only to the new March 21, but also by the use of new Paschal tables
Computus is the calculation of the date of Easter in the Christian calendar. The name has been used for this procedure since the early Middle Ages, as it was one of the most important computations of the age....


The name of the bull consists of the first two words of the bull, which starts: "Inter gravissimas pastoralis officii nostri curas…" ("Among the most serious duties of our pastoral office…").

The bull refers to "the explanation of our calendar" and to a canon related to the dominical letter. To accompany the bull there were six chapters of explanatory rules ('canons'), and some of these (canons 1, 2, 4) refer to a book entitled Liber novæ rationis restituendi calendarii Romani (not extant) for a fuller explanation of the tables than that contained in the canons (or the bull). Because the bull, canons, and book all refer to each other, they must have been written at roughly the same time, printed at the same time (March 1), and distributed to the several countries together.

These canons enabled the computation of Easter dates in the reformed ('restored') Gregorian calendar, and gave two calendar-listings saints' days
Roman Catholic calendar of saints
The General Roman Calendar indicates the days of the year to which are assigned the liturgical celebrations of saints and of the mysteries of the Lord that are to be observed wherever the Roman Rite is used...

, one for the 'year of correction' (1582) and another for the entire new Gregorian year. The bull, canons, and calendars were reprinted as part of the principal book explaining and defending the Gregorian calendar, Christoph Clavius, Romani calendarii a Gregorio XIII. P. M. restituti explicatio (1603), which is tome V in his collected works Opera Mathematica (1612).


The version of "Inter gravissimas" included by Christoph Clavius in his work explaining the Gregorian calendar contained these dating clauses: "Anno Incarnationis Dominicae M. D. LXXXI. Sexto Calend. Martij, Pontificatus nostri Anno Decimo. ... Anno à Natiuitate Domini nostri Iesu Christi Millesimo Quingentesimo Octuagesimo secundo Indictione decima,". These clauses include four years:
  • "Anno Incarnationis Dominicae M. D. LXXXI." (In the year of the Incarnation of the Lord 1581) is the year beginning . is the traditional date of the conception, annunciation
    The Annunciation, also referred to as the Annunciation to the Blessed Virgin Mary or Annunciation of the Lord, is the Christian celebration of the announcement by the angel Gabriel to Virgin Mary, that she would conceive and become the mother of Jesus the Son of God. Gabriel told Mary to name her...

    , and incarnation
    Incarnation (Christianity)
    The Incarnation in traditional Christianity is the belief that Jesus Christ the second person of the Trinity, also known as God the Son or the Logos , "became flesh" by being conceived in the womb of a woman, the Virgin Mary, also known as the Theotokos .The Incarnation is a fundamental theological...

     of Jesus
    Jesus of Nazareth , commonly referred to as Jesus Christ or simply as Jesus or Christ, is the central figure of Christianity...

  • "Pontificatus nostri Anno Decimo" (In the tenth year of our pontificate) is the year beginning . Gregory XIII was elected pope on .
  • "Anno à Natiuitate Domini nostri Iesu Christi Millesimo Quingentesimo Octuagesimo secundo" (In the year from the Nativity of our Lord Jesus Christ 1582) is the year beginning using the modern beginning of the year. It marks the beginning of year 1582 if that year began on , the traditional date of the birth or nativity of Jesus
    Nativity of Jesus
    The Nativity of Jesus, or simply The Nativity, refers to the accounts of the birth of Jesus in two of the Canonical gospels and in various apocryphal texts....

  • "Indictione decima" (Indiction
    An indiction is any of the years in a 15-year cycle used to date medieval documents throughout Europe, both East and West. Each year of a cycle was numbered: first indiction, second indiction, etc...

     10) is the year beginning , which agrees with modern reckoning.

All of these years agree that the bull was dated February 24, 1582, using the modern beginning of the year.


Gregory's reform was enacted in the most solemn of forms available to the Church, but the bull had no authority beyond the Catholic Church and the Papal States
Papal States
The Papal State, State of the Church, or Pontifical States were among the major historical states of Italy from roughly the 6th century until the Italian peninsula was unified in 1861 by the Kingdom of Piedmont-Sardinia .The Papal States comprised territories under...

. The changes which he was proposing included changes to the civil calendar
Civil calendar
In any country, the civil calendar is the calendar, or possibly one of several calendars, used within that country for civil, official or administrative purposes. The civil calendar is almost always used for general purposes by people and private organizations....

 over which he had no authority (except in the Papal States). The text of the bull recognized this by giving what amounted to orders to the clergy and those "presiding over churches": but in contrast, where the text addresses the civil authorities ("kings, princes and republics"), it "asks", "exhorts" and "recommends" the new calendar changes. The changes required adoption by the civil authorities in each country to have legal effect.

For dates on which various countries adopted the Gregorian reforms, see Gregorian calendar.

The Nicene Council of 325 sought to devise rules whereby all Christians would celebrate Easter on the same day. In fact it took a very long time before Christians achieved that objective (see Easter
Easter is the central feast in the Christian liturgical year. According to the Canonical gospels, Jesus rose from the dead on the third day after his crucifixion. His resurrection is celebrated on Easter Day or Easter Sunday...

 for the issues which arose). However, the bull Inter gravissimas, which was not immediately adopted by many European countries, became the law of the Catholic Church. It was not recognised, however, by Protestant Churches
Protestantism is one of the three major groupings within Christianity. It is a movement that began in Germany in the early 16th century as a reaction against medieval Roman Catholic doctrines and practices, especially in regards to salvation, justification, and ecclesiology.The doctrines of the...

 nor by Orthodox Churches and others. Consequently, the day on which Easter was celebrated by different Christian Churches again diverged.

External links

  • Wikisource English translation of Inter gravissimas
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