King Felipe VI and Queen Letizia joined crowds of devotees waving Spanish and Vatican flags in Cibeles Square for a service filled with religious symbolism.
In his homily, Pope Leo said Spaniards should not look at religion as “a museum of the past to be visited, but a school of faith from which to draw even today”.
The mass comes on day two of Pope Leo’s seven-day visit to Spain, a traditional Catholic bastion where religious observance has been declining sharply in recent years as in much of western Europe.
A huge logistical and security operation was in place for the event, after which the pope led a traditional procession along a route lined with white and yellow carnations – the Vatican flag colours.
Organisers said more than 1.2 million people were attending in the square and the surrounding area.
Nico Aldeanueva, 28, who was visiting from Philadelphia in the United States, said the pope was “a very unifying force in a moment where we have division across so many different fronts”.
“We have, it seems like, never-ending conflict, and for the time being, here you get to hit pause and get to enjoy the moment and feel the faith.”
Ana Milagros, 64, who was waving a Vatican flag, said she thought the US-born pope seemed “approachable” and “very sincere”.
“There is a lot of polarisation and differences in politics, in social matters, in the economy,” she said, adding: “The pope is trying with this visit… to help all of us.”
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Focus on migration
Later on Sunday, Leo will meet the leading lights of culture, sport and the economy to foster dialogue between faith and modern civil society.
Around 56 percent of Spaniards identify as Catholic compared to 90 percent in the 1970s, according to a survey by the Centre for Sociological Research, an autonomous government body.
On Saturday, 500,000 attendees gathered outside Real Madrid’s Bernabeu stadium for a prayer vigil that stretched into the night.
Leo kicked off his visit with pomp and ceremony at a reception in Madrid’s royal palace, where he called for an end to “polarising narratives” and “sterile simplifications”.
The pope also praised Spain, whose left-wing government has sparred with his native United States as well as Israel over wars in the Middle East, for its “active commitment to peace and solidarity among peoples”.
Leo is due to visit Barcelona on Tuesday and Wednesday, where he will bless the Sagrada Familia basilica’s recently completed tower, which made it the world’s tallest church.
His trip will end with a focus on migration on Thursday and Friday in the Canary Islands, a key destination for irregular arrivals.
