Pope Francis arrives to celebrate Mass in Revolution Square in Havana, Cuba, Sunday, Sept. 20, 2015. Pope Francis opens his first full day in Cuba on Sunday with what normally would be the culminating highlight of a papal visit: Mass before hundreds of thousands of people in Havana's Revolution Plaza.  (Tony Gentile/POOL via AP)

Pope Francis meets Castro

While most Cubans are nominally Catholic, fewer than 10 percent practice their faith.