Are you familiar with the story of how, on this date in 1917, three shepherd children claimed to have seen an apparition of the Virgin Mary on multiple occasions in Fatima, Portugal? This vision became popularly known as "Our Lady of Fatima." The site became a destination for mass pilgrimage when the kids said that Our Lady of Fatima had promised a miracle upon her final appearance in October 1917. Seventy thousand people allegedly flocked to the site on that day. But more enduringly, the children also claimed that Our Lady of Fatima had shared with them three "secrets."
Two of the three shepherd children died in the Great Spanish Flu epsidemic of 1918-1920. But the oldest child, Lucia, lived until 2005 and became a nun. Lucia revealed two of the three secrets publicly in a memoir she wrote as an adult. The first secret was a vision of Hell. The second concerned instructions on how to save souls from Hell, as well as prophecies about the potential conversion of Russia to Catholicism. But the third "secret" remained a tantalizing mystery. Lucia had revealed it to the Vatican, but with instructions that it be revealed to the world only after 1960. But in 1960, the Vatican announced that it was "most probable the Secret would remain, forever, under absolute seal." This proclamation, not surprisingly, had the opposite of its intended effect. It greatly increased interest in the secret and prompted speculation about it's nature: was it an apocalyptic vision of nuclear annihilation?
It was in this context that I first heard about the "third secret of Fatima" in the early 1980s, after Pope John Paul II publicly proclaimed his belief in Our Lady of Fatima. The Cold War context renewed speculation that the hidden "third secret" concerned a vision of world-wide nuclear annihilation. The Vatican ultimately revealed the third secret in June 2000, however. In the end it was "merely" a vision about the death of the Pope and other religious figures.
I once watched a very interesting 1 hour documentary on this whole thing which aired on The History Channel. It was an episode of the series "History's Mysteries" and has now been posted (in segments) on You Tube. You can watch part 1 by clicking HERE.