Between May and October of 1917, three shepherd children, Lúcia Santos and her cousins Jacinta and Francisco Marto reported visions of the Virgin Mary in the Cova da Iria fields outside the hamlet of Aljustrel, very close to Fatima, Portugal. They had this experience on the 13th day of each month at approximately the same hour. Lúcia described seeing Mary as "brighter than the sun, shedding rays of light clearer and stronger than a crystal glass filled with the most sparkling water and pierced by the burning rays of the sun."
According to Lúcia's account Mary confided to the children three secrets, known as the Three Secrets of Fatima. She exhorted the children to do penance and to make sacrifices to save sinners. Most important, Lúcia said Mary asked them to say the Rosary every day, reiterating many times that the Rosary was the key to personal and world peace. Many young Portuguese men, including relatives of the visionaries, were then fighting in World War I.
Thousands of people flocked to Fatima and Aljustrel in the ensuing months, drawn by reports of visions and miracles. On August 13, 1917, the provincial administrator Artur Santos (no relation), believing that the events were politically disruptive, intercepted and jailed the children before they could reach the Cova da Iria that day. Prisoners held with them in the provincial jail later testified that the children, while upset, were consoled by the inmates, and then led the inmates in saying the Rosary.
On October 13, 1917, the final in the series of the apparitions of 1917, a crowd believed to be approximately 70,000 in number, including newspaper reporters and photographers, gathered at the Cova da Iria in response to reports of the children's prior claims that on that day a miracle would occur "so that all may believe". It rained heavily that day, yet countless observers reported that the clouds broke, revealing the sun as an opaque disk spinning in the sky and radiating various colors of light upon the surroundings, then appearing to detach itself from the sky and plunge itself towards the earth in a zigzag pattern, finally returning to its normal place, and leaving the people's once wet clothing now completely dry. The event is known as the "Miracle of the Sun".
Columnist Avelino de Almeida of O Século (Portugal's most influential newspaper, which was pro-government in policy and avowedly anti-clerical),  reported the following: "Before the astonished eyes of the crowd, whose aspect was biblical as they stood bare-headed, eagerly searching the sky, the sun trembled, made sudden incredible movements outside all cosmic laws-the sun 'danced' according to the typical expression of the people." Eye specialist Dr. Domingos Pinto Coelho, writing for the newspaper Ordem reported: "The sun, at one moment surrounded with scarlet flame, at another aureoled in yellow and deep purple, seemed to be in an exceeding fast and whirling movement, at times appearing to be loosened from the sky and to be approaching the earth, strongly radiating heat". The special reporter for the October 17, 1917 edition of the Lisbon daily, O Dia, reported the following: "...the silver sun, enveloped in the same gauzy gray light, was seen to whirl and turn in the circle of broken clouds...The light turned a beautiful blue, as if it had come through the stained-glass windows of a cathedral, and spread itself over the people who knelt with outstretched hands...people wept and prayed with uncovered heads, in the presence of a miracle they had awaited. The seconds seemed like hours, so vivid were they."
No movement or other phenomenon of the sun was registered by scientists at the time. According to contemporary reports from poet Afonso Lopes Vieira and schoolteacher Delfina Lopes with her students and other witnesses in the town of Alburita, the solar phenomena were visible from up to forty kilometers away. The three shepherd children, in addition to reporting seeing the actions of the sun that day, also reported seeing a panorama of visions, including those of Jesus, the Blessed Virgin Mary, and of Saint Joseph blessing the people.