Pope Francis begins a two-day pilgrimage on Friday to the holy site of Fatima in central Portugal to mark the centenary of the first visions of the Virgin Mary.
Here are five key facts about Fatima, one of Catholicism's most revered sites:
The site where the Madonna is said to have appeared to three shepherd children between May and October 1917 has become a major centre of worship.
Between 50,000 and 70,000 faithful flock to the shrine every year on the anniversary of the last apparition on October 13, 1917, when witnesses claimed to have seen the sun "dance in the sky".
Many make the last few hundred metres of their journey on their knees as a sign of gratitude to the Virgin for favours they believe she has granted them.
At the shrine, pilgrims suffering from an illness or disability buy wax models of the body parts that are ailing, as part of a ritual of prayer for well-being and good health.
The pope will on Saturday make two of the three shepherd children believed to have seen the Madonna in Fatima saints.
The canonisation of Francisco Marto and his sister Jacinta Marto will coincide with the 100th anniversary of the first of the reported apparitions of the Virgin.
Francisco and Jacinta -- who died in an influenza pandemic while they were still children several years after the visions -- were beatified, the final step before sainthood, by Pope John Paul II in 2000.
The beatification process for their cousin Lucia dos Santos, the oldest of the three children, began in 2008, three years after her death at the age of 97.
The Church believes the Virgin gave the children three messages, the so-called three secrets of Fatima, which were written down by Lucia in several memoirs written years after the apparitions.
The first secret concerned a vision of hell, seen by believers as a call for prayer and a denunciation of the persecution of the Catholic Church.
The second secret predicted the outbreak of World War Two and asked that the Church consecrate Russia, which was undergoing the Bolshevik Revolution in 1917, to the Virgin.
The third secret, which was only made public by the Vatican in 2000, foretold the attempted assassination in Rome of Pope John Paul II on May 13, 1981, on the anniversary of the first apparition in Fatima.
Pope Benedict XVI later gave an updated interpretation of the third secret, saying it could include the suffering the Church would have to endure following sexual abuse scandals that were shaking the Vatican at the time.
Pope Francis will be the fourth pope to visit Fatima.
Pope John Paul II, a three-time visitor to the site, credited the Virgin of Fatima with saving his life in the 1981 assassination attempt.
After he visited the shrine in 1982 to give thanks, a bullet extracted from his body was placed alongside diamonds in a gold crown worn by a statue of the Virgin.
Around eight million faithful are expected to visit Fatima in 2017, up from 6-7 million last year, making it one of the most visited Marian shrines in the world.
The shrine in Lourdes in southwestern France receives around six million visitors per year while the Guadalupe shrine in Mexico city welcomes some 20 million visits annually.