Pope Leo XIV will make a high-profile visit to Nicaea on Nov. 28 as he marks 1,700 years since the Council of Nicaea, a meeting of bishops that helped define Christianity’s most widely recited creed. The pope’s trip, part of his first major foreign journey as pope, will pair commemoration with an effort to underscore unity at a site remembered for both theological agreement and later fracture.
Church historian Giovanni Maria Vian, coauthor of “La scommessa di Costantino,” described Nicaea as a foundational milestone, saying, “The occasion is very, very important — the first global, ecumenical council in history and the first form of creed acknowledged by all the Christians.” Vian’s framing ties the anniversary to the council’s breadth and to the creed’s role as a shared point of reference across Christian traditions.
Leo will commemorate the anniversary with Patriarch Bartholomew, the spiritual leader of Eastern Orthodox Christianity, as the event’s modern significance extends beyond Catholic-Orthodox relations. The story of Nicaea, in the way it is told by historians and church observers, has remained a common reference point for Catholic, Orthodox and most historic Protestant groups that accept the creed, even as later splits and reforms changed how Christians practice and argue about doctrine.
The council’s historical importance also rests on how it was organized: Constantine convened the meeting after consolidating control over the Roman Empire following years of civil war. Although Constantine would not formally convert to Christianity until the end of his life, by 325 he had already shown tolerance and favor toward a Christian sect that had emerged from the last major period of Roman persecution, and the arrangement placed a powerful political leader at the center of shaping church policy.
The council involved an unprecedented gathering of at least 250 bishops from around the Roman Empire, and the core dispute it confronted was not simply whether Christians believed in a Trinity. The “Trinitarian Controversy,” as it is sometimes called, focused on how the Son relates to the Father—an argument that took its influential name from Arius, an Egyptian priest associated with a doctrine that depicted Jesus as the highest created being rather than equal to God.
Constantine convened the bishops to resolve the theological clash, and the bishops nearly unanimously supported a creed endorsed by the emperor. The creed declared Jesus to be “true God” and condemned those who promoted Arian ideas, while describing Jesus as equal to the Father and as of “one substance” using the Greek term “homoousios,” described in the reporting as a word drawn from Greek philosophy rather than the Bible.
The council’s effort at compromise also extended to the calendar used to determine Easter, which the reporting says had been controversial. According to the account, the council approved a calendar favored by Arian sympathizers by setting Easter for the Sunday after the first full moon of spring—an outcome that left each side with something it could claim as a win. David Potter, author of “Constantine the Emperor” and a professor at the University of Michigan, said, “The Council of Nicaea was an extraordinary diplomatic success for Constantine, because he got the two sides to agree,” and he added, “I’ve often thought that it’s nice that a piece of imperial legislation is read out every Sunday.”
While the creed and the Easter formula aimed to align Christians across doctrinal and practical lines, the anniversary also highlights what the reporting describes as ominous language about Jews included in the council’s Easter decision. Potter said, “Institutional antisemitism was absolutely a feature of the church,” and he noted that harsh language was common during ancient religious disputes among early Christians, Jews and pagans, but that it helped set a precedent for centuries of persecution of Jewish minorities in Christian lands.
Even with those agreements, the account says the settlement did not settle everything: Arius made a comeback and returned to political favor, and doctrinal debate continued for generations, including in the streets of Constantinople. Later, a different emperor convened another council in 381 that affirmed an expanded Nicene creed with added lines describing the church and the Holy Spirit; the reporting says this final version became the standard text used today and is sometimes called the Nicene-Constantinopolitan Creed.
In the modern commemoration, Pope Leo’s agenda also reflects how Nicaea’s legacy intersects with contemporary inter-church relations. While much of historic Christianity accepts the Nicene Creed, the reporting notes that some Oriental Orthodox churches accept the creed but reject later councils, and it says Leo plans to meet representatives of two Oriental Orthodox groups—Armenian Apostolic and Syriac Orthodox churches—during his time in Turkey. The Catholic and Eastern Orthodox churches, meanwhile, split in the 11th century over issues that included an addition to the creed regarding the Holy Spirit, and many Protestant movements later split over other questions, even though many continued to affirm the Nicene Creed.
Still, the anniversary is being framed by some clergy and theologians as a reminder of unity’s possibility rather than as a catalog of failure. Rev. John Burgess, a systematic theology professor at Pittsburgh Theological Seminary and a scholar on Eastern Orthodoxy, said, “An event like the 1,700 years of Nicaea is really the celebration not of a reality but of a hope — of what Christians at their best know ought to be the case, that there is a deep call to unity.”