Pope Francis will give mass today on Revolution Square in Havana, the biggest event of his trip to Cuba, with nearly a million people expected to attend.
The pope, who arrived on the communist island yesterday, will address the crowd beside a towering sculpture of his fellow Argentine Che Guevara's iconic silhouette, following in the footsteps of his predecessors John Paul II and Benedict XVI.
Cuban President Raul Castro and Argentina's Cristina Kirchner will be among those in attendance.
The pope's eight-day tour, which will also take him to the United States for the first time, follows the announcement of the US-Cuban rapprochement, which paved the way for the estranged neighbors to renew diplomatic relations in July.
Francis, the first Latin American pontiff, helped facilitate that moment in secret negotiations.
The pope received a tropically warm welcome on arrival in the Cuban capital Saturday afternoon, when tens of thousands of people braved the heat and humidity to greet him with dancing, cheers and banners along the route from the airport to the Vatican nunciature.
Castro welcomed him with a lengthy speech that hit repeatedly on some of the pope's favorite themes: caring for the planet, fighting inequality and promoting peace.
After mass, the pope will meet with Castro, then preside over vespers at Havana Cathedral before holding an unscripted exchange with young Cubans -- a demographic feeling the pain of the communist island's difficult economic transition.
Francis may also meet Castro's older brother and predecessor Fidel, the 89-year-old father of Cuba's 1959 revolution.
"If it happens, it will happen (Sunday). And we'll get you the necessary information," Vatican spokesman Federico Lombardi told journalists Saturday.
Benedict XVI met Fidel when he visited the island in 2012, six years after the longtime leader handed power to Raul amid a health crisis.
On arriving yesterday Francis asked Raul to convey his "sentiments of particular respect and consideration" to Fidel.
Lombardi said the central themes for the pope's visit would be the fractious conflicts tearing apart the Middle East and elsewhere, migration and the need to help those who flee their homes, and the importance of dialogue in building bridges.
Before departing on his trip, Francis met with a family of Syrian Christians from Damascus whom the Vatican has taken in to put the pope's message into action.
