The route to Santa Maria Maggiore recalls centuries-old traditions.

Francis, who died on Monday at 88, last year had approved guidelines to make his funeral a less grand affair than those of his predecessors. The centuries-old rites, however, still involved Catholic pageantry and 250,000 participants, the Vatican said.

At the Mass, the pope’s body was placed in a simple wooden coffin before the mourners as a choir sang a psalm. Between the songs, the clerics led prayers in different languages — English, Spanish, Italian — as crowds around the square, some who had waited since dawn, watched the service on large TV screens.

Among those paying their respects were Mr. Trump; former President Joseph R. Biden Jr.; and President Javier Milei of Argentina, where Francis was born. Refugees, for whom Francis advocated throughout his 12-year papacy, also attended the service, as did many young people.

Here is what else to know:

• Simplified ceremony: The changes Francis introduced for a papal funeral last year reflect his view of the pope as a humble pastor rather than a powerful figure, although the rites are still on a grand scale. Accompanying the Mass were the sober melodies of Gregorian chants, sung by the pope’s personal choir.

• Francis’ burial: After the Mass, a vehicle will transport Francis’ wood coffin to St. Mary Major, a papal basilica in Rome that the pope loved. A group of “poor and needy” people will greet his body at the steps, the Vatican said. Then, he will be buried during a private ceremony in a tomb with a one-word inscription “Franciscus.”

• Choosing a successor: After the burial, the focus will turn in earnest to the election of the next pope by the College of Cardinals. Several names have surfaced as possible successors.

• Remembering Francis: Cardinal Giovanni Battista Re, in a homily on Francis’ legacy, called him “a pope among the people.” Bible readings that Francis chose for the ceremony affirmed Christian messages of hope and inclusivity.

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On Saturday, the vehicle carrying Pope Francis’ coffin will detour in the direction of the Papal Basilica of Santa Maria Maggiore, where Francis wanted to be buried. The Vatican said on Saturday that the car was a converted popemobile that had been used in a previous trip.

People lined the streets along the way. The route passes the Chiesa del Gesu, the mother church of the Society of Jesus, the religious order to which Francis belonged. It also passes the Colosseum, the 2,000-year-old Roman arena where a 17th-century fresco that was restored three years ago showed that it had also been a sacred site for Christian worship.

At Santa Maria Maggiore, a group of “poor and needy” people will be waiting on the steps, the Vatican said this week. That was fitting, the Vatican added, because St. Francis of Assisi renounced his wealth to live in poverty, and the pope “had chosen the name Francis to never forget them.”

To date, 80 of the 266 popes to serve over nearly 2,000 years have been canonized. Another 11 are on a waiting list of sorts, having been beatified, the penultimate step to sainthood.

Getting there involves years of investigation and review by the church, particularly the Dicastery for the Causes of Saints. Vatican officials and consultants examine candidates’ goodness, holiness and devotion to God and carefully scrutinizes their writings. Those who pass muster are declared “venerable.”

The next step is beatification, which requires the dicastery to accept the validity of a miracle brought about by the intercession of the candidate. After that, the Vatican must accept the validity of a second miracle attributed to the person’s intercession for them to be declared a saint. The pope makes the final decision on canonization.

The most recent popes to be been canonized are John XXIII and John Paul II. They became saints at a joint ceremony that Francis presided over in 2014.

For most of the church’s history, decades usually passed between a person’s death and the beginning of a push for their canonization.

From 1588 to 1978, the average time span between a person’s death and sainthood was 262 years, according to Rachel McCleary, a researcher at Harvard University. That dropped to just over 100 years during the last three papacies, in part because John Paul II shortened the waiting period to begin a cause for sainthood, as the process is known, to five years after a person’s death.

Even that can be waived. At John Paul II’s 2005 funeral, which hundreds of thousands attended, banners and cheers rose from the mourners saying, “Santo, subito,” or “Sainthood now.” His successor, Benedict XVI, waived the waiting period, allowing John Paul to be canonized nine years after his death.

After a Vatican report published in 2020 found that John Paul may have ignored accusations of sexual abuse against the disgraced former prelate Theodore E. McCarrick, critics wondered whether he the pontiff been made a saint too soon.

The meeting in Rome came at a critical moment, just as the United States had presented a suggested plan for a cease-fire in Ukraine’s war with Russia and a postwar plan that would give Russia effective control over all of the lands it has illegally seized since the invasion began three years ago. The plan includes a major reversal of American policy: a formal American recognition that Crimea is Russian territory, even if Ukraine and the rest of Europe maintain that it remains part of Ukraine.

Mr. Trump had made clear he wanted his first trip overseas in this term to be to the Middle East, starting with Saudi Arabia, the site of his initial visit during his first term in office.

But then Pope Francis died. And so Saturday morning, made his way to Vatican City to pay his respects at the pontiff’s funeral.

As the ceremonies began, Mr. Trump was surrounded by European leaders he has been denouncing as freeloaders unwilling to pay their share of the continent’s defense, and leaders of the European Union, which he said was “formed in order to screw the United States.”

On his way over to Italy on Friday, Mr. Trump told reporters on Air Force One that he was attending the funeral “out of respect” for Francis, noting, “I won the Catholic vote.”

The president’s schedule does not allow much time for meetings, or even many casual “pull asides,” the term diplomats use for planned, brief encounters. Mr. Trump was able to chat a bit when he arrived.

The seating plan released by the Vatican had guests seated in their group in alphabetical order based on their country’s name in French. That put Mr. Trump in the front row between the leaders of Finland and Estonia, and just down from President Emmanuel Macron of France.

The schedule calls for Mr. Trump to leave Rome less than three hours after the ceremony begins, and to fly to Newark to spend the night at his nearby golf club.

Mr. Trump’s every handshake and conversation at the funeral is being watched for meaning. Ursula von der Leyen, the president of the European Commission, the executive arm of the European Union, was sitting a few chairs down from Mr. Trump, and White House reporters traveling with the president, but kept at a considerable distance, reported that the two appeared to chat, funereal protocols aside. In the past three months, Ms. von der Leyen was conspicuously absent from the leaders visiting the White House.

“He was a pope among the people, with an open heart toward everyone,” Cardinal Re said beside Francis’ coffin from the steps of St. Peter’s Square. “He was also a pope attentive to the signs of the times and what the Holy Spirit was awakening in the church.”

As the cardinals arrayed around him prepared to head into a conclave next month to choose Francis’ successor, Cardinal Re, 91, avoided obvious political overtones. But by highlighting Francis’ pastoral and inclusive approach, and his humble style, Cardinal Re’s tribute sought to remind the tens of thousands of faithful at St. Peter’s Square, the dozens of assembled heads of state and dignitaries, and — perhaps most important — the cardinals responsible for picking Francis’s replacement what made him such an esteemed figure inside and outside the church.

“The guiding thread of his mission was also the conviction that the church is a home for all, a home with its doors always open,” Cardinal Re said.

He said that Francis had spread the faith with a sense of joy, a “great spontaneity and an informal way of addressing everyone,” and a spirit of “welcome and listening.” But Francis also “truly shared the anxieties, sufferings and hopes of this time of globalization.”

With President Trump seated a few yards away, Cardinal Re recalled the late pope’s trip to the border between Mexico and the United States, one of his many “gestures and exhortations in favor of refugees and displaced persons,” when Francis spoke of the need to “build bridges, not walls.”

Cardinal Re said that Francis’ pastoral style and “resolute personality” had immediately made a mark on the church, and that the pontiff had been “eager to be close to everyone, with a marked attention to those in difficulty, giving himself without measure, especially to the marginalized, the least among us.”

The Cardinal spoke of Francis’ rise through the hierarchy to become pope and said his decision to take the name Francis, after the medieval saint dedicated to caring for the poor, “immediately appeared to indicate the pastoral plan and style on which he wanted to base his pontificate.”

He described Francis as a simple pastor who until his last day followed in the footsteps of Jesus, who loved his flock “to the point of giving his life for them,” because he believed it was better to give than to receive.

Cardinal Re walked through Francis’ milestones in the church, his protection of the environment, his work healing wounds between religions, including a document on human fraternity that he signed with Muslim leaders in the United Arab Emirates, and his frequent calls to stop war and conflict. He recalled how Francis physically reached out to the world’s peripheries, seeking to heal wounds and spread seeds of faith.

“The outpouring of affection that we have witnessed in recent days following his passing from this Earth into eternity tells us how much the profound pontificate of Pope Francis touched minds and hearts,” Cardinal Re said.

He said the enduring image of Francis would be that of Easter Sunday, the day before his death when, despite being obviously ailing, he came to a balcony overlooking St. Peter’s Square to deliver his blessing and then greeted the crowd.

Recalling that Francis often ended talks with an invitation to pray for him, the cardinal concluded, “Dear Pope Francis, we now ask you to pray for us.”

The first reading, from the Acts of the Apostles 10: 34-43, is part of a pivotal moment in the early church when Peter, one of Jesus’ disciples and a man whom Catholics consider the first bishop of Rome, learns through a vision that the good news of the Gospel message is not just for the original followers but for a wider world.

“This is the universality of the gospel and a welcome to all,” said Gemma Simmonds, an author and senior research fellow at the Margaret Beaufort Institute of Theology in Cambridge, England.

“That is very much what Pope Francis wanted to emphasize,” added Ms. Simmonds, who is also a sister in the Congregation of Jesus, a Catholic religious order for women. “He was constantly talking about going beyond the conventional boundaries of the church and speaking to people that the church had originally excluded.”

The second reading, from St. Paul’s letter to the Philippians, 3:20–4:1, argues that a Christian’s true citizenship is not on Earth but in heaven. The passage explains death as a transformation of the human body, which it calls the “lowly body,” through Jesus, into what Paul calls the “heavenly body.”

The third Gospel reading, John 21: 15-19, recounts a conversation between Jesus and Peter after Jesus’ resurrection, in which the disciple is restored to faith and given the leadership role in the early church. Three times in the passage, Jesus asks Peter if he loves him. Jesus also asks Peter to “tend my sheep” and “feed my lambs.”

According to the biblical account, the conversation takes place after Peter betrayed Jesus in the run-up to his crucifixion by denying that he knew him. Experts said that in choosing that Gospel reading, Francis — as he had during his ministry — was making a deliberate reference to human vulnerability and the need for God’s grace.

“I see all of these readings as a traditional affirmation of the Christian message of forgiveness and hope and affirmation and the messages that Pope Francis emphasized in his papacy,” said Tina Beattie, a professor emerita of Catholic Studies at the University of Roehampton in London.

Also known as plainsong or plainchant, this has been the official musical language of the church for over 1,000 years: austere, somber, unaccompanied and monophonic, meaning that everyone sings the same vocal line, as opposed to more complex polyphony.

“For truly solemn occasions, the best way to express the continuity of the church’s musical tradition is just to have simple chant,” James D. Wetzel, the director of music at the Church of St. Vincent Ferrer in Manhattan, said in an interview. “The church promotes the golden age of Renaissance polyphony, Mozart, Duruflé, modern settings. But pride of place is given to chant.”

So at Francis’ funeral, the main components of the Requiem Mass that anchor the service — like the opening Introit (“Requiem aeternam dona eis, Domine”), Kyrie, Sanctus and Agnus Dei — and sections including the litany of names of saints are being chanted in Latin. The Sistine Chapel Choir, the Pope’s personal choir, is the featured ensemble.

At some other state religious services, like the funeral of Queen Elizabeth II or the coronation of King Charles III, the music is a virtuosic mix of the familiar, obscure and new — meant to be awe-inspiringly different from everyday worship.

But the plainchant melodies at Francis’ funeral will be known to churchgoing Catholics. The music’s sober, unadorned style fits with the ways in which he simplified the elaborate papal funeral rites.

There will be occasions during the funeral for choral singing other than plainchant, but the Vatican, in keeping with its standard practice, has not identified the composers, or if any new music has been written for the occasion. The church has a tradition of priest-composers, including directors of the Sistine Chapel Choir, whose settings may have been selected. It is likely that the psalm “Sicut cervus” (“Like the deer that yearns for running streams”) will be performed in Palestrina’s luminous setting, one of the great examples of Renaissance polyphony.

By intention, however, there will be no obvious musical innovations.

“This is the time for the oldest traditions,” Mr. Wetzel said. “Even with Pope Francis, who was not afraid of surprises or upsetting the apple cart, the music sung at his funeral will be entirely Catholic, with a capital C.”

In the movie “Conclave,” which dramatized the death of a pope and the tensely political process of choosing his successor, the dean was named Cardinal Lawrence and portrayed by a principled yet questioning Ralph Fiennes.

Unlike in the movie, however, Cardinal Re will not run the conclave to select the next pope. He will not even attend, since only cardinals below the age of 80 can cast a ballot for the pope in the Sistine Chapel, though he will still play an important role in the run-up to the gathering.

That embrace of modesty is etched throughout his legacy.

He sought to overhaul, and at times rejected, papal pageantry and the formality long associated with the Roman Catholic Church. He chose his papal name from St. Francis of Assisi, who dedicated his life to the poor. He rode in a Ford Focus, wore basic black shoes and took meals in a communal cafeteria. For his living quarters, he opted for a guesthouse next to St. Peter’s Basilica in Vatican City instead of the more ornate papal apartments.

And he set to work on simplifying papal funerals.

In April 2024, Francis approved a liturgical book that included a new set of rules emphasizing that “the funeral of the Roman pontiff is that of a pastor and disciple of Christ and not of a powerful person of this world,” Archbishop Diego Ravelli, master of apostolic ceremonies, said when the book was published.

This week inside St. Peter’s, where tens of thousands of faithful came to pay their last respects, Francis’ body lay in a coffin that was placed low to the ground instead of on an elevated bier. Instead of nesting the coffin inside two additional coffins before burial, as was done for popes in the past, Francis is being laid to rest in one.

The departure from earlier papal burials is “totally in line with how Pope Francis led,” said Mathew Schmalz, a professor of religious studies at the College of the Holy Cross in Worcester, Mass. He added of Francis, “He wanted a papacy that was more reachable, that was down to earth and was able to engage with Catholics in their daily lives.”

Of course, for a pope, simplicity is relative. While some of the funerary pomp and ceremony has been scaled back, Francis was still the religious leader to over a billion Catholics, and some traditions that date back centuries will endure. His funeral is being attended by dignitaries from around the world, and crowds have gathered in and around St. Peter’s Square for the funeral.

Whereas many popes have been buried at St. Peter’s, Francis will be interred at the Papal Basilica of Santa Maria Maggiore, a 17th-century chapel dear to him in Rome. His tomb, according to his will, is inscribed with a single word: “Franciscus.”

He was accompanied by his wife, Melania, and a clutch of senior aides. But his predecessor, former President Joseph R. Biden Jr. and his wife, Jill, flew in on their own.

Considering that Mr. Trump had recently stripped Mr. Biden of his security clearances, and regularly denounces him, it is understandable that they did not share a ride to Rome. When former President Jimmy Carter died in December, Mr. Trump said he had passed away “a happy man” in the knowledge that “he wasn’t the worst. President Joe Biden was.”

Mr. Biden has often talked about his Roman Catholic upbringing. He saw Pope Francis briefly at a summit meeting in Italy last June, weeks before the disastrous debate with Mr. Trump that led to his decision to drop out of the presidential race. Mr. Biden had talked about returning to Rome to get the pope’s blessing just before leaving the White House, but canceled the trip because of the Los Angeles wildfires in January.

Asked on Air Force One on the flight to Rome on Friday evening whether he planned to talk with Mr. Biden at the funeral, Mr. Trump sounded surprised that his predecessor was attending. “It’s not high on my list,” he said. “It’s really not.”

The contrast with the 2005 papal funeral was stark. Mr. Bush was eager to ensure that Mr. Clinton was part of the full presidential party. Not only did the two men attend the funeral together, the former president sat in on the highly classified presidential daily brief on the flight over.

But the joined-at-the-hip act ended in the evening. Mr. Bush went to sleep early, around the time Mr. Clinton was just heading out. One night during the visit, Mr. Clinton was dining in a private room at a small, highly rated Italian restaurant when he realized that many of the White House reporters who had covered him as president were eating at a big table in the main dining room.

Naturally, he called us in to join him for dessert and espresso, and told stories until the early hours of the morning.