The Pope best known for his reformation of the Julian calendar to the Gregorian calendar may be tied to the origin of April Fools Day. Now WE know em


Pope Gregory XIII was born Ugo Boncompagni January 7, 1502 in Bologna (northern Italy), where he grew up to study law and graduated in 1530.

Ugo later taught jurisprudence for some years, and his students included notable figures such as Cardinals Alexander Farnese, Reginald Pole and Charles Borromeo. He had an illegitimate son before taking his holy orders.

At the age of thirty-six he was summoned to Rome by Pope Paul III, under whom he held successive appointments as first judge of the capital, abbreviator, and vice-chancellor of the Campagna.

Pope Paul IV attached him as datarius to the suite of Cardinal Carlo Carafa.

Pope Pius IV then made him Cardinal-Priest of San Sisto Vecchio and sent him to the Council of Trent.

He also served as a legate to Philip II of Spain, being sent by the Pope to investigate the Cardinal of Toledo. It was here that he formed a lasting and close relationship with the Spanish King, which was to become very important in his foreign policy as Pope.


Election as Pope

Upon the death of Pope Pius V in 1572, the conclave chose Cardinal Boncompagni, who assumed the name of Gregory XIII in homage to the great reforming Pope, Gregory I (590–604), surnamed the Great.

It was a very brief conclave, lasting less than 24 hours. Many historians have attributed this to the influence and backing of the Spanish King. Gregory XIII’s character seemed to be perfect for the needs of the church at the time. Unlike some of his predecessors, he was to lead a faultless personal life, becoming a model for his simplicity of life. Additionally, his legal brilliance and management abilities meant that he was able to respond and deal with major problems quickly and decisively, although not always successfully.


The Gregorian calendar

Pope Gregory XIII is best known for his reformation of the calendar, with the aid of Jesuit priest/astronomer Christopher Clavius, who is credited as the calendar’s chief architect.

The reason for the reform was that the average length of the year in the Julian calendar was too long – it treated each year as 365 days, 6 hours in length, whereas calculations showed that the actual mean length of a year is slightly less (365 days, 5 hours and 49 minutes).

As a result, the date of the actual vernal equinox had slowly (over the course of 13 centuries) slipped to 10 March, while the computus (calculation) of the date of Easter still followed the traditional date March 21.

This was verified by the observations of Clavius, and the new calendar was instituted when Gregory decreed, by the papal bull Inter gravissimas of February 24, 1582, that the day after Thursday, October 4, 1582 would be not Friday, October 5, but Friday October 15, 1582.

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The new calendar duly replaced the Julian calendar, in use since 45 BC, and has since come into universal use. Because of Gregory’s involvement, the reformed Julian calendar came to be known as the Gregorian calendar.

However, more than a century passed before Protestant Europe accepted the new calendar.

Denmark, the remaining states of the Dutch Republic, and the Protestant states of the Holy Roman Empire and Switzerland adopted the Gregorian reform in 1700–01. By this time, the calendar trailed the seasons by 11 days.

Great Britain and its American colonies reformed in 1752, where Wednesday, September 2, 1752 was immediately followed by Thursday September 14, 1752.

While some Eastern Orthodox national churches have accepted the Gregorian calendar dates for feast days that occur on the same date every year, the dates of all movable feasts (such as Easter) are still calculated in the Eastern Orthodox churches by reference to the Julian calendar.


During his pontificate, Pope Gregory XIII fostered cultural patronages associated with his papacy. He strengthened many ecclesiastical and diplomatic envoys to Asia, namely the islands of Japan and the Philippines.  He was also the first Pope to bestow the Immaculate Conception as Patroness to the Philippine Islands on February 9, 1579.

Pope Gregory XIII died April 10, 1585 at the age of 83.


April Fools Day

Sometimes referred to as All Fools’ Day

Many historians suggest that the restoration of January 1 by Pope Gregory XIII as New Year’s Day of the Gregorian Calendar in the 16th century was responsible for the creation of April Fools Day.

In the Middle Ages, up until the late 18th century, New Year’s Day was celebrated on March 25 (Feast of the Annunciation) in most European towns.

In some areas of France, New Year’s was a week-long holiday ending on April 1.

As a result, some historians suggest that April Fools originated because those who celebrated New Years Day on January 1 made fun of those who continued to celebrate New Years day on other dates.

 Now WE know em


Detail of the tomb of Pope Gregory XIII celebrating the introduction of the Gregorian calendar.

Detail of the tomb of Pope Gregory XIII celebrating the introduction of the Gregorian calendar.





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