Pope Francis had a busy day in Havana, as he said mass before a crowd of thousands at the iconic Revolution Square. “Whoever wishes to be great must serve others, not be served by others,” the Pope said during his homily.

Afterward, Pope Francis met with Fidel Castro during a 40 minute meeting. “The two men discussed world affairs and religion, in what the Vatican called an 'informal and friendly' encounter,” the BBC reported.

According to Fox News Latino, Pope Francis brought Castro three books: Two by an Italian priest, Alessandro Pronzato, and one by Fidel's former Jesuit teacher, the Rev. Amando Llorente. Llorente taught at Colegio de Belen, where Fidel was a student, and the book was a collection of his preachings.

Pope Francis is due to fly to Washington on Tuesday to continue a visit through the United States.