MADRID — Pope Leo XIV celebrated a public Mass before an estimated 1.2 million people in Cibeles Square on Sunday, the largest gathering of his weeklong visit to Spain and the centerpiece of the first papal trip to the country in 15 years.

The turnout, tallied by the Vatican and local organizers, turned the plaza best known as Real Madrid's title-celebration site into the stage for an American pontiff pressing a message of social unity into a country whose politics, church and migration debate are each under strain. Leo addresses Spain's parliament Monday, an intervention in a European argument over polarization that has hardened since his predecessor's last European tour.

The Madrid welcome

Leo arrived at the square in his white popemobile as crowds tossed flower petals and waved flags, Al Jazeera reported. The mayor handed him the key to the city. In the guestbook, the pope wrote, "May Madrid continue to be a welcoming and inclusive city, where social life is inspired by true human values."

Sunday's Mass followed a Saturday evening prayer vigil at Plaza de Lima that PBS NewsHour, citing organizers, said drew about 500,000 people, many of them young. It was at that vigil and during his airport welcome by King Felipe VI, Queen Letizia and Prime Minister Pedro Sánchez that Leo set out the trip's theme.

"Today, the temptation to gain popularity by fanning the flames of polarization seems to have grown rather than diminished, and human dignity continues to be violated," Leo said, according to PBS. He urged political leaders to set aside "the divisive and polarizing narratives of your societal reality and history" and help Europe "overcome sterile simplifications through the fruitful appreciation of complexity."

A polarized host

Sánchez's Socialist-led government is contending with a series of corruption scandals, and the conservative Popular Party and Vox have demanded his resignation, PBS reported. Spain has bucked the broader Western trend by moving to grant legal status to potentially hundreds of thousands of immigrants already working in the country, a policy Sánchez has defended by pointing to an aging workforce and low birthrate.

Leo's Monday address to a joint session of the Congress of Deputies and the Senate is the first such speech by a pope, according to PBS. The pontiff invoked Spain's 800-year Moorish past and named Toledo and Córdoba as historical "centers of dialogue between languages, religions and knowledge."

The church's open wound

Leo confirmed he will meet with clergy abuse survivors during the trip, telling reporters, "Abuses are still an open wound," PBS reported. The Spanish Catholic hierarchy has belatedly begun reckoning with decades of abuse and cover-up. The king referenced a recently launched church-state reparations system in his airport remarks while insisting such cases "neither are nor can be representative of the immense ecclesial community."

The trip, which runs June 6 through June 12, also takes Leo to Barcelona, where he will celebrate Mass at the Sagrada Familia basilica on the centenary of the death of its architect, Antoni Gaudí, NBC News reported. He will close the visit in the Canary Islands, the Spanish archipelago the United Nations has identified as the endpoint of one of the world's deadliest migration routes, and is expected to toss a wreath into the sea at the Las Palmas port to honor migrants killed during the Atlantic crossing.

The counterpoint

Leo's call to set aside "divisive and polarizing narratives" lands on a parliament whose largest opposition bloc has spent months arguing that Sánchez's migration policy and corruption record are themselves the source of national division. No right-leaning outlet appeared in today's reporting, and the Popular Party and Vox had not publicly responded to the pontiff's Saturday remarks by Sunday evening. Protests of the trip were expected, PBS reported, without quantifying them.

The pope, who got his start as a missionary in Peru and is the first American pontiff, offered a lighter note en route to Madrid. Asked about the 2026 World Cup, Leo told reporters, "I will certainly support the U.S.," NBC News reported. Italy did not qualify. Monday's parliamentary address will test whether his weekend message survives contact with Spain's elected politicians.