Pope Leo XIV formally opens his pontificate with Mass in St Peter’s Square

Pope Leo XIV officially opened his pontificate as history’s first American pope on Sunday, presiding over an inaugural Mass in St Peter’s Square before tens of thousands of people, presidents, patriarchs and princes in a ceremony that blended ancient ritual, evocative symbols and a nod to modern-day celebrity.

Leo launched the celebration by taking his first popemobile tour through the piazza, a rite of passage that has become synonymous with the papacy’s global reach and mediatic draw, used at home and abroad to bring popes close to their flock.

The 69-year-old Augustinian missionary smiled and waved from the back of the vehicle as the bells of St Peter’s Basilica rang.

Leo appeared to choke up when the two potent symbols of the papacy were placed on him – the pallium wool stole over his shoulders and the fisherman’s ring on his finger – as if the weight of responsibility had just sunk in.

He turned his hand to look at the ring and seal and then clasped his hands in front of him in prayer.

The crowd cheered and plenty of Peruvian, American and Holy See flags mixed with flags of other nations and banners.

Tens of thousands of people had earlier streamed into St Peter’s Square. Starting at dawn, civil protection crews in neon uniforms funnelled pilgrims into quadrants in the piazza while priests and patriarchs hurried into St Peter’s Basilica to get ready for the Mass.

US vice president JD Vance, one of the last foreign officials to see Pope Francis before he died, paid his respects at the Argentine pope’s tomb when he arrived in Rome late on Saturday, and was heading the US delegation honouring Chicago-born Leo.

Diplomatic protocol also dictated the dress code. While most wore black, the handful of Catholic queens and princesses – Charlene of Monaco and Letizia of Spain among others – wore white in a special privilege allowed them.

Three dozen of the world’s other Christian churches sent their own delegations, headed by patriarchs, reverends, ministers and metropolitans, while the Jewish community had a 13-member delegation, half of them rabbis.

Leo started the day by taking his first tour through the piazza in the popemobile.

It was here that Francis made his last popemobile ride on Easter Sunday, and it was on the back of a popemobile that Francis’ coffin was taken across Rome last month to its final resting place.

Leo seems more timid than Francis. But all eyes will be on how he manages the throngs of pilgrims, tourists and curiosity-seekers, and the babies who will inevitably be passed up to him for a blessing.

After the tour in the square, Leo went into the basilica to begin the solemn ceremony to inaugurate his ministry in a series of rites that emphasise the service that he is called to perform in leading the Catholic Church.

He prayed first at the tomb of St Peter, considered to be the first pope, under the basilica’s main altar, and then processed out into the piazza for the Mass.

Peruvian President Dina Boluarte is one of about a dozen heads of state attending, as well as Ukrainian President Volodymyr Zelensky.

US seminarian Ethan Menning, 21, from Omaha, Nebraska, wrapped himself in an American flag to celebrate.

“Rome always felt like home for a Catholic, but now coming here and seeing one of our own on the throne of Peter, it almost makes Jesus himself more accessible,” he said.

Kalen Hill, a pilgrim from the US, got to St Peter’s soon after the gates opened on Sunday and said he never expected an American would lead the 1.4-billion strong church.

“I would say all the Americans are emotional about it,” he said. “It is really powerful for American Catholics who sometimes feel separated from the world church to be brought in and included in this community through Pope Leo.”

During the Mass, Leo received the two potent symbols of the papacy: the lambswool stole, known as a pallium, and the fisherman’s ring.

The pallium, draped across his shoulders, symbolises the pastor carrying his flock as the pope carries the faithful.

The ring, which becomes Leo’s official seal, harks back to Jesus’ call to the apostle Peter to cast his fishing nets.

The other symbolically important moment of the Mass is the representational rite of obedience to Leo.

Whereas in the past all cardinals would vow obedience to the new pope, more recent papal installations involve representatives of cardinals, bishops, priests, deacons, nuns, married couples and young people participating in the rite.

Another change from the past is that Sunday’s Mass is not a coronation ceremony, which used to involve the pope receiving a tiara, but is merely known as a “Eucharistic Celebration for the start of the Petrine ministry of the Bishop of Rome”.

In the days since his historic election, Leo has already sketched out some of his key priorities as pope.

In his first foreign policy address, he said the Holy See’s three pillars of diplomacy were peace, justice and truth.

In his first major economics address, he emphasised the Catholic Church’s social doctrine and the search for truth.

Leo has vowed all efforts to find peaceful ends to the wars in Ukraine, Gaza and elsewhere.

But as a priority, he has also identified the challenges to humanity posed by artificial intelligence, making the parallel to the challenges to human dignity posed by the industrial revolution that were confronted by his namesake, Pope Leo XIII, who was pope from 1878-1903.

After the homily and at the end of the Mass, Leo will offer a final blessing and then go into the basilica to greet the heads of the more than 150 official delegations attending.

Security was tight, as it was for Francis’ funeral on April 26, which drew an estimated 250,000 people.

Rome authorities planned for another 250,000 on Sunday.

The piazza and main boulevard leading to it, and two nearby piazzas, were set up with giant television screens, and dozens of portable toilets have been erected in a nearby park.