The apparition of Our Lady to the three shepherd children in 1917 in the little Portuguese town of Fatima is commemorated on May 13. Between May 13, 1917, and October 13, 1917, she made six appearances to Lucia, 9, and her cousins Francisco, 8, and his sister Jacinta, 6.

The story of Fatima begins in 1916, a year before the Communist revolution would send Russia and later Eastern Europe into six decades of oppression under militant atheist governments, and against the backdrop of the First World War, which had introduced Europe to the most horrific and powerful forms of warfare yet seen.

The three children were tending the family sheep in the field when they saw a resplendent figure appear. "I am the Angel of Peace," the figure declared as she made two more appearances to them that year, urging them to regularly pray for the conversion of sinners and to accept the pains that the Lord had allowed them to endure as atonement for their transgressions.

Then, on May 13, 1917, the children were approached by a vision of "a woman all in white, more brilliant than the sun," who said, "Please don't be afraid of me, I'm not going to harm you." When Lucia questioned her where she came from, she said, "I come from Heaven."

She also disclosed that the children would suffer, particularly due to their friends' and families' lack of faith, and that Lucia would live longer in order to propagate her message and devotion to the Immaculate Heart, while the two younger children, Francisco and Jacinta, would shortly be taken to Heaven.

In response to Lucia's query at the last apparition, the woman said, "I am the Lady of the Rosary."

70,000 people showed up to see the apparition that same day, having been promised by the woman that she would prove the apparitions were real. There was no question in their minds about the authenticity of the apparitions as they witnessed the sun move in an amazing zigzag pattern and complete three circles around the sky. The apparitions received approval from the Bishop by 1930, and the Church recognized them as genuine.

The children received messages from Our Lady during the apparitions, warning them of the terrible trials—war, starvation, and persecution of the Church and the Holy Father—that the world would face in the twentieth century if atonement for sins was not made. In an attempt to bring about world peace and prevent trials, she urged the Church to pray and offer sacrifices to God.

Three prophetic "secrets" were revealed by Our Lady of Fatima; the first two were previously disclosed and dealt with the vision of hell and the souls that are imprisoned there; the third was a request for a fervent devotion to Mary's Immaculate Heart; the prediction of the Second World War; and, lastly, the revelation of the enormous harm that Russia would cause to humanity by rejecting Christianity and embracing Communist totalitarianism.

The third "secret," which wasn't made public until 2000, spoke of the persecutions mankind would face in the last century and said that "the good will be martyred; the Holy Father will have much to suffer; various nations will be annihilated." It has been suggested that the 1981 murder attempt on Pope John Paul II, which happened on May 13, the 64th anniversary of the apparitions, counts among the suffering of the popes of the 20th century.