On Monday, the Vatican released the official program for Pope Francis' two-day visit to Portugal in May, where he'll celebrate the centenary of the Fatima Marian apparitions and make a brief stop at an air base to meet the country's president.

Francis will likely make a stop at his favorite Roman basilica, Saint Mary Major, sometime before leaving Rome at 2 p.m. May 12.

He'll land at the air base in Monte Real around 4:20 p.m. local time, where he'll be greeted by an official welcoming ceremony and meet with the president of Portugal, Marcelo Rebelo de Sousa, before making his way to Fatima.

After his meeting with the president, the Pope is scheduled to stop by the chapel of the air base for a moment of prayer before boarding a helicopter that will take him to the Fatima's multi-use stadium.

From there, he'll hop inside an open car and drive to the Shrine of Our Lady of Fatima. Once he arrives around 5:30 p.m., Pope Francis will head to the Chapel of the Apparitions inside the sanctuary, where he'll recite a prayer.

He'll then bless the candles in the chapel and offer a special greeting, marking his first public speech of the trip, before praying the rosary with faithful.

The next day, May 13, which marks the first apparition of Mary to the three shepherd children Lucia, Francisco and Jacinta, Francis will meet with Portugal's Prime Minister António Costa at the city's Casa "N.S. do Carmo" hotel-convent.

Francis will then head to the Basilica of Our Lady of the Rosary in Fatima, which sits next to the official Shrine, to say Mass. After the celebration, he'll greet sick and disabled persons who are present.

Lunch will then be served with the Portuguese bishops at the Casa "N.S. do Carmo" before the Pope heads back to the Monte Real air base for his official farewell ceremony.

He's scheduled to leave around 3 p.m. local time, arriving to Rome's Ciampino airport around 7 p.m. local time. As usual, he'll likely pay another visit to the basilica of St. Mary Major to pray and leave flowers before heading back to the Vatican.

Of all Marian apparitions, those relating to Our Lady of Fatima are among the most famous. On May 13, 1917, siblings Francisco and Jacinta Marto – age 9 and 7 – and their cousin, 10-year-old Lucia dos Santos, took their sheep to graze near the Portuguese town of Fatima when they saw a figure of a woman dressed in white and holding a rosary.

After this first appearance, the Virgin Mary then appeared to the children on the 13th of every month from May until October. The message of the Fatima apparitions can be summarized primarily as a call to repentance and prayer.

In 1930, the Catholic Church proclaimed the supernatural character of the apparitions and a shrine was erected at Fatima. It was visited by Pope Paul VI May 13, 1967, and later by Popes John Paul II and Benedict XVI.

St. John Paul II had a particularly strong devotion to Our Lady of Fatima. After a harrowing assassination attempt in 1981, he credited his survival to her miraculous intervention. As a sign of his gratitude, he placed the bullet from the failed assassination in her crown.

"Pray for the brother who shot me, whom I have sincerely forgiven. United to Christ, as a priest and victim, I offer my sufferings for the Church and the world," Pope John Paul II said on that occasion.