ROME – As Pope Francis prepares to arrive in Fatima, Portugal, today, the apparitions of our Lady of the Rosary outside the village to three young illiterate shepherds in 1917 remain both among the most beloved, and controversial, of the Catholic Church-approved Marian apparitions.

In a sense, ever since Mary appeared in the field called Cova de Iria a hundred years ago, there have been two Fatimas in the popular imagination.

On the one hand, there’s a devotion focused on Mary’s appearances to three illiterate shepherd children, who in many ways portray the definition of what Pope Francis calls the peripheries of society, as further proof of God’s special love for the simple ones of the earth.

The message for those who see Fatima under this light is it’s a reminder of the basic traits of Christian life: Faith, hope, and charity; including prayer and penance and the need for conversion.

On the other hand, there’s the darker and harder-edged Fatima, the one focused on speculation about the third part of the famed secret, that carries an apocalyptic undertone, speculation about Russia, nuclear annihilation, the murdering of the “bishop in white,” and the great apostasies of the Catholic church after the Second Vatican Council (1962-65).

Seeing that the Vatican and the past nine popes have treated it as a genuinely miraculous site, and not just a fable made up in early 20th century Portugal, here’s a round-up of everything you need to know about “Cold War Mary,” as Pope Francis sets off to his first visit to Portugal.

The who, what and when

In the year 1917, Portugal was going through the hardships of World War I, the Great War. Although Portugal suffered relatively few combat deaths – only about 12,000 Portuguese soldiers died as a result of the fighting, including colonial subjects from Africa – tens of thousands of civilians died of starvation, while over 130,000 people died during the Spanish flu pandemic which began in 1918.

In addition, with the Portuguese First Republic which began in 1910, extreme secularism and persecution of Catholics reared its head. Churches were plundered, convents were attacked, and clergy killed. An estimated 1,800 religious, including priests, monks and nuns, were killed in a span of five years (1911-1916).

It was against this backdrop that the Virgin Mary appeared to Lúcia Dos Santos and her cousins Francisco and Jacinta Marto.

Mary first appeared, on May 13, 1917; when asked who she was and where she came from, the “lady dressed in white,” as Dos Santos described her, said she came “from heaven,” and promised to reveal her identity at a later date.

Though she withheld her identity, she asked the children to return every 13th for the following five months, and urged them to pray the rosary every day “in order to obtain peace for the world” and the end of World War I.

“Fatima becomes a model for late twentieth and twenty-first century apparitions, not only in establishing a pattern of appearances that will be repeated in subsequent Marian visitations (e.g., 13th of the month), but in laying out a template for end-time speculation,” Marian expert Sandra L. Zimdars-Swartz of the University of Kansas said.

There’s a pattern, she told Crux, of Mary calling for a set of devotions that, if observed, can forestall the disaster that looms, such as war, famine, and persecution of the Church.

“But if people fail to respond, then there will be further warnings, in the form of signs, that will remind Mary’s children that the end is near,” the author of Encountering Mary: from La Salette to Medjugorje said.

During the second apparition, Mary promised to take Francisco and Jacinta to heaven soon, while Lucia would remain on earth “sometime longer” to help establish a global devotion to the Immaculate Heart. The two youngest seers died in 1919 and 1920, after becoming seriously ill with the Spanish flu, which killed 20 million people.

Lucia would grow to become a Carmelite nun, and the devotion to Mary’s Immaculate Heart grew exponentially. In his video message to the people of Portugal ahead of his visit, Francis mentioned it, showing it’s still a very current thing.

“I will give you all to Our Lady, asking her to whisper to each one of you: ‘My Immaculate Heart will be your refuge and the way that will lead you to God,’” he said.

The “secret” of Fatima

On the third apparition, in July, Mary gave the shepherds a message, which has come to be known as the “Great Secret” of Fatima. Lucia wrote the first two parts in her 1941 memoirs. The third part, usually described as the third secret, was written by the seer around the same time, but wax-sealed and sent to the Vatican, with instructions of not being opened until at least 1960.

Though St. John XXIII and other popes read the text, it wasn’t revealed to the world until the year 2000, when Pope John Paul II decided to do so. It included a series of notations from Cardinal Joseph Ratzinger, who back then was the head of the Vatican’s doctrinal office, and who would eventually become Pope Benedict XVI.

Some devotees believe the version released by the Vatican is incomplete, omitting details about the end of the world and a condemnation of modernizing currents in the church. Some also believe that the secret was supposed to be revealed in 1960, and that the fact that it wasn’t is part of a decades-long cover-up.

Perhaps the fact that in 1960 the Vatican issued a press release stating that it was “most probable the secret would remain, forever, under absolute seal,” fueled the speculation that ensued about what this meant for the content of the secret.

Sister Lucia dos Santos, one of the three children who saw Our Lady of Fatima in 1917 and who lived in the Carmelite convent of St. Teresa in Coimbra, Portugal, until her death in 2005 at 97, is pictured in this 2000 file photo. In 2008, Pope Benedict XVI lifted the normal five-year waiting period to begin the canonization process of Sister Lucia. (Credit: CNS photo/Paulo Carrico, EPA.)
Sister Lucia dos Santos, who lived in the Carmelite convent of St. Teresa in Coimbra, Portugal, until her death in 2005 at 97, is pictured in this 2000 file photo. In 2008, Pope Benedict XVI lifted the normal five-year waiting period to begin her canonization process. (Credit: CNS photo/Paulo Carrico, EPA.)

Yet the Vatican in December 2001 issued a press release asserting that Lucia had informed then-Archbishop Tarcisio Bertone, at the time Ratzinger’s top aide, that the secret had been fully revealed.

It was also during the third apparition, on July 13, that the Virgin showed them “a sea of fire,” which they understood to be Hell, included in what was revealed as the first part of the secret.

“Plunged in this fire were demons and souls in human form, like transparent burning embers, all blackened or burnished bronze, floating about in the conflagration … amid shrieks and groans of pain and despair, which horrified us and made us tremble with fear,” Lucia wrote in her memoirs.

By the time of the third apparition, word had spread about what was going on. On this day, the three children found it difficult to go from their homes to Cova de Iria.

“The crowd pressed against them and shouted out requests for the children to present to the Virgin, many if not most of which concerned the hardships caused by fathers, sons, brothers, and husbands being sent to war, not to mention anxiety about their safe return,” Zimdars-Swartz said.

“To put it simply, in 1917 and the years immediately following, Fatima was a place one came to seek healing,” she added. It wasn’t until much later, when Lucia revealed the first two parts of the secret that the event took an apocalyptic undertone.

For devotees, the Marian expert explained, Fatima’s cosmic drama seemed to give a place to the two world wars of the 20th century, to provide a framework for understanding the rise of communism with its mention of Russia, and to give believers a role to play in changing the course of historical and political events through their devotional practices.

The children missed the fourth apparition because the then mayor of Fatima kidnapped them for two days, threatening to kill them by throwing them into boiling oil, hoping they would stop talking about the apparitions.

However, seeing that they wouldn’t budge, he eventually freed them. The Virgin appeared to them a few days later, asking the seers to be in the Cova on the thirteenth day of the following month.

In September, the Lady once again urged the shepherds to pray the rosary daily so that the war would come to an end, and promised that on the last day, she would be joined by Jesus and St. Joseph, which occurred.

A month later, the final apparition took place, with a crowd estimated at 70,000 people being there to see what has become known as the miracle of “the dancing sun.”

RELATED: Fatima and the Atheists

After introducing herself as “Our Lady of the Rosary” and promising the end of the war, the Virgin opened her hands towards the sun, which in turn began to spin and change colors. She also asked for a chapel to be built on the site, which is where the shrine the pope will visit on Friday and Saturday is located.

Thirteen years later, the bishop of Leira-Fatima declared the apparitions to be worthy of belief. However, he did not recognize the miracle of the sun.

The nay-sayers

Since apparitions of Mary, Jesus, and other major Catholic figures are considered by the Church to be “private revelations,” belief in them is not mandatory, as opposed to things like belief in Mary’s perpetual virginity or the Trinity. The latter are considered “divine revelations,” as they are found in the Bible or the Church’s tradition.

Many remain skeptical about the fact that in 1917 the Virgin appeared to three little shepherds, gave them a secret, produced the miracle of the dancing sun, and that she cracked the earth open to show them the sufferings of Hell, despite the fact that every pope since Benedict XV has deemed them credible.

Yet the decision to believe in this Marian apparition, or any of those approved by the local bishop, which unless under extraordinary circumstances is the Church authority with the power to do so, is not the most debated aspect of the events that took place in the Cova de Iria.

Most of the debates turn around what is known as the third part of the Fatima secret, with some conspiracy theories saying it hasn’t been revealed in full or refusing to believe the interpretation that was given by Ratzinger.

It was in the years immediately following the Second World War, that part of the Secret of Fatima began to circulate widely.

As Zimdars-Swartz told Crux, with its apparent prediction of the Second World War and with Mary’s call to dedicate Russia to her Immaculate Heart and the warning that if this did not happen there would be more war and persecution of the church and pope, the secret became central to the perception of the meaning of Fatima.

It also made this apparition an important part of the Church’s arsenal against the perceived threat of communism.

“But the Fatima scenario of cosmic drama has proven particularly adaptable to changing historical circumstances. Any number of perceived contemporary ills, from secularism to pervasive moral perversity can be (and are) substituted for communism,” Zimdars-Swartz said.

Pope Francis, who’s often spoken about the end of times, regularly quoting the 1907 book by Robert Benson, Lord of the World, has generally stayed out of this argument and the notion of Mary as carrier of warnings too.

For him, the significance of Fatima is as a reminder of Mary’s maternal love for humanity, and her role of introducing the world to Christ, placing the accent on its spiritual importance.

Furthermore, his strong Marian devotion is rooted in hope and peace, prayer and conversion, as the tweet he sent out on the eve of the trip shows: