In an ongoing dialogue with Ecumenical Patriarch Bartholomew of Constantinople, the successor of St. Andrew the Apostle and “first among equals” among the bishops of the Eastern Orthodox Church, Pope Francis has expressed his belief that Catholics and Orthodox will one day attain full communion. Eastern Orthodox — as opposed to Eastern-rite Catholics who differ from Latin-rite Catholics in custom and liturgical practices but accept the primacy of jurisdiction of the Bishop of Rome — gradually separated from Rome in the Middle Ages and are today composed of a variety of Orthodox churches, the largest of which is the Russian Orthodox Church with nearly 100 million members. Orthodox and Catholics both accept the first seven Ecumenical Councils of the Church as well as the seven sacraments and apostolic succession, but differ in key areas as well, most notably the primacy of the pope. 

Another notable area of difference between them is the date of Easter. In 2024, Catholics and much of the rest of the world celebrate Easter on March 31, while the Orthodox celebrate Easter on May 5. The difference is due to the fact that most Orthodox churches use the Julian calendar introduced by Julius Caesar in 45 B.C. and the Catholic Church uses the Gregorian calendar introduced by Gregory XIII’s 1582 papal bull Inter Gravissimas (“Among the Greatest Concern”). Developing an accurate calendar can be a challenge, as a year or amount of time it takes the earth to make a complete revolution around the sun cannot be neatly organized into days and months. Such a revolution takes nearly a quarter of a day longer than 365 days, so calendars must be adjusted for this difference or be increasingly off year-to-year. Both the Julian and Gregorian calendars were efforts to account for the movements of the sun and the moon, with the Gregorian calendar being the more successful effort to do so.

Easter, or the celebration of the resurrection of Our Lord, is the most important of all liturgical times, however, in the earliest centuries, the Christian churches celebrated it on different dates. The First Ecumenical Council of Nicaea of 325 resolved the issue by decreeing that the universal Church would celebrate Easter on the first Sunday after the full moon following the beginning of Spring. Hence, year-to-year, the earliest possible date for Easter could be March 22 and the latest April 25. 

Errors in the Julian calendar in use at the time, however, became evident, as the calculated year was too long by 11 minutes and 14 seconds. Church leaders were aware of this inaccuracy and believed that not celebrating Easter on the precise day indicated by the Council of Nicaea was a scandal. (The inaccurate calendar created problems in the secular world as well, adversely affecting the timing of the planting of crops and the navigation of ships during different seasons of the year.)

Seeking to correct the problem, Pope Gregory XIII via a papal bull removed 10 days from the calendar in 1582. People went to bed Oct. 4 and woke up Oct. 15. (Hence, the Julian calendar falls behind the Gregorian calendar, about 13 days currently, but increasing to 14 days in 2100.)

Catholic countries such as Spain, Italy, Portugal and the Polish-Lithuanian Commonwealth and the Spanish colonies immediately adopted the new calendar. Protestant countries began adopting it in the 1700s, including colonial America in 1752. Holdouts included Russia, which remained on the Julian calendar until 1917, and Greece, which remained on the Julian calendar until 1923. 

While many Orthodox churches accept the Gregorian calendar for fixed religious feasts, all except the Orthodox Church of Finland use the Julian calendar for movable feasts such as Easter. In recent dialogue with Pope Francis, however, Ecumenical Patriarch Bartholomew indicated his support for finding a common Easter date, believing the first such common date should be in 2025. However, the possibilities for success may be remote, due to fracturing within the Orthodox church community. In 2018, for example, the Russian Orthodox Church announced that it had severed ties with the Ecumenical Patriarchate of Constantinople after Bartholomew confirmed he intended to recognize the independence of the Orthodox Church of Ukraine. Father Hugh Barbour of St. Michael’s Abbey in Southern California added that Russia’s 2022 invasion of Ukraine has created further divisions between leaders of Orthodox churches and the Ukrainian government, which wants to impose a change over to the Gregorian calendar for fixed feasts on the Orthodox church “exacerbating the situation horribly and setting back any hope of reunion within Orthodoxy.”

Regardless of the political situation, Father Hugh continued, while worldwide reunion is desirable it will more likely be attained “bit by bit on a local level.” He explained, “While Orthodox churches have the same faith and worship, showing marvelous coherence in liturgy and the doctrine of the faith, their jurisdictions are local and national rather than universal. This decentralized power structure makes them hard to deal with ecumenically. The Catholic Church, in contrast, is a papal monarchy able to act from a single center.”

He added that while the date of Easter has a symbolic importance, it is not the key issue that papal primacy is. He said, “The Roman Church historically never has had any difficulty with Eastern Catholics using the older Julian calendar if they desire. In fact, there are some benefits.” The observance of the Orthodox or Julian date of Christmas on Jan. 7, as well as the different Easter date, separates them from the secular, commercialized observance of such holidays “making them more tranquil and exclusively religious. That’s often why they like it.”

He continued, “What is more, the witness to unity in Christian worship has already been asserted recently in the Holy Land where the Catholic Latin Patriarchate of Jerusalem has largely adopted the Julian ‘Orthodox’ date of Easter so that all the Christians of the Apostolic Jurisdictions there show unity in a place where unity is crucial to their survival. This is a deep reason to consider a common date of Easter, suggested already by the Second Vatican Council 60 years ago.”