While exploring different places, one can appreciate them, especially where there is an extensive array of objects; however, remembering and explaining them all can be challenging. St. Peter’s Basilica in the Vatican is an example of such a place. It houses numerous sculptures depicting former popes or saints. Some of these figures not only played pivotal roles in the Catholic Church but also held significance in a broader context. One such figure was Pope Gregory XIII.

Pope Gregory XIII, born as Ugo Boncompagni in 1502, in Bologna, Italy, was the 226th pope of the Roman Catholic Church. He ascended to the papacy in 1572, and held the position until his death in 1585. Before becoming Pope, he served as the Governor of Fano and later as the papal legate to Spain. The latter activity helped him to be elected pope in a conlcave that lasted for less than 24 hours.

Statue of Pope Gregory XIII at the St. Peter’s Basilica, Vatican by Camillo Rusconi (1658–1728)

Pope Gregory XIII was the one who commissioned the Gregorian Calendar, named after him, to make necessary corrections to its predecessor, the Julian Calendar. The reform was necessary to realign the calendar year with the solar year, ensuring a more accurate reflection of Earth’s orbit around the Sun, which used to occur in the Julian Calendar. According to the Julian Calendar, a year was 365.25 days long. In fact, the solar year is a bit shorter than that. The Gregorian Calendar refined the length of the year to be about 365.2425 days. The difference in the length of the year between the Julian and Gregorian calendars was about 0.18 hours, which is approximately 10.8 minutes. It doesn’t make a difference on an annual scale; however, over several hundred years of using the Julian Calendar, it created a time gap between the calendar year and the solar year (overestimation of the solar year).

The Julian Calendar, named after Julius Caesar, was introduced in 45 BCE. It was used for 1,527 years! To synchronize the calendar with astronomical realities, a ten-day correction was introduced, along with new time counting. On the implementation of the Gregorian Calendar October 4, 1582, was followed by October 15, 1582. This adjustment recalibrated the calendar and brought it in harmony with the changing seasons.

The adjustments made during the introduction of the Gregorian Calendar made the calendar more accurate compared to the solar year, but there was still a tiny difference. In the Gregorian Calender like in the Julian Callender every fourth year is a leap year, except however for years divisible by 100 but not by 400. This meticulous adjustment ensures that the calendar year closely aligns with the solar year, preventing a gradual drift over time.

The adoption of the Gregorian Calendar varied among countries, and it did not happen simultaneously worldwide. Some of the first countries to adopt the Gregorian Calendar were those under Catholic influence, as the calendar reform was initiated by the Catholic Church. First to adopt were the Catholic countries like Italy, Spain, Portugal and Poland. In the latter it was later dropped and then reintroduced. Russia was one of the last major countries to adopt the Gregorian Calendar. The switch occurred after the Russian Revolution in 1917. The Julian Calendar was in use in Russia until January 31, 1918, when they transitioned to the Gregorian Calendar. The last country to officially adopt the Gregorian Calendar was Saudi Arabia. It made the switch from the Islamic Hijri Calendar to the Gregorian Calendar on October 1, 2016. Saudi Arabia’s decision to adopt the Gregorian Calendar was part of a series of economic and social reforms aimed at aligning the country with global standards. Before this change, Saudi Arabia was one of the last countries to use a purely lunar-based calendar for civil purposes. The Gregorian Calendar has become the standard civil calendar worldwide. While the Gregorian Calendar is predominant in secular contexts, various cultures and religions continue to observe alternate calendars.