Pope Leo prays for unity at historic Nicaea site

Pope Leo XIV attends a ceremony marking the 1700th anniversary of the First Council of Nicaea held in the ruins of submerged basilica, revealed in 2014 after water levels receded in Lake Iznik. Chris McGrath/Anadolu via Getty Images hide caption

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Chris McGrath/Anadolu via Getty Images

IZNIK, Turkey —On the second day of his inaugural foreign trip, Pope Leo XIV visited the site where early Christian leaders met 1,700 years ago for the First Council of Nicaea — the gathering that produced the creed still spoken in churches today.

The first American pope prayed alongside Ecumenical Patriarch Bartholomew, the spiritual leader of the world's Eastern Orthodox Christians, amid the archaeological ruins of the lakeside church where bishops met in 325 to resolve divisions threatening to tear the early Church apart.

"We must strongly reject the use of religion for justifying war, violence, or any form of fundamentalism or fanaticism," Pope Leo said in his speech at the site on the shore of the tranquil Iznik Lake. "Instead, the paths to follow are those of fraternal encounter, dialogue and cooperation."

Pope Leo has used the trip to press for unity — among Christian denominations, and also among other religions and communities. In a speech along Turkish President Recep Tayyip Erdogan on Thursday, the Pope warned that the division and polarization seen in the world today is placing the very future of humanity at stake.

Emperor Constantine convened the First Council of Nicaea, bringing bishops from across the Roman Empire to resolve a doctrinal crisis over how to explain Jesus' relation to God. Christians had been persecuted for some 250 years, until a decision by Emperor Constantine allowed the faithful to worship in freedom across the Roman Empire. Constantine saw a unified Church as essential to stabilizing an empire emerging from civil war.

Pope Leo XIV takes part in a prayer service with Bartholomew I, Ecumenical Patriarch of Constantinople, near the excavations of the ancient Basilica of Saint Neophytos on Nov. 28, 2025 in Iznik, Turkey. Chris McGrath/Getty Images Europe hide caption

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Chris McGrath/Getty Images Europe

The fiercest dispute came from Arius, an Alexandrian priest who argued that Jesus, though exalted, was the highest created being, but not equal to God.

The council, whose bishops had gathered from across the Roman Empire, ultimately rejected his teachings and affirmed that Jesus is "of one substance" with the Father — language that forms the basis of the creed recited by catholics today, which begins: "I believe in one God, the Father almighty …".

This aerial photograph shows remains of the sunken Byzantine Basilica of Saint Neophytos on the shore of Lake Iznik, which Pope Leo XIV visited on Friday, Nov. 28th. OZAN KOSE/AFP via Getty Images hide caption

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OZAN KOSE/AFP via Getty Images

The exact location of the council was only discovered about 11 years ago, when public workers taking aerial photographs of Lake Iznik shared images with Turkish archaeologist Mustafa Sahin. "It was under about eight feet of water," he told NPR.

Locals know the ruins well; in low water, swimmers sometimes rest on the stones. As the shoreline has since receded, the full footprint of the basilica — its apse and dozens of graves — now sits on dry land.

The Church remained mostly united until the Great Schism of 1054, which split Catholic and Eastern Orthodox Christianity over theological disputes and power struggles between Rome and Constantinople - modern day Istanbul.

At the historic site on Friday, Pope Leo XIV and Patriarch Bartholomew held a joint silent prayer over the exposed ruins. Ahead of the anniversary, Leo released an apostolic letter emphasizing the creed as a "common heritage of Christians," written when "the wounds inflicted by the persecutions of Christians were still fresh."

On Saturday the Pope and the Patriarch will sign a joint declaration in a modern show of unity.