First, a caveat: Anyone with a strong grasp of Latin—or a distaste for Dan Brown novels—will warn others not to get too excited about the name of this papal library. Archivum Secretum looks like it would refer to a “secret” archive, but the translation is actually closer to “private archive,” and it serves as a place where the personal documents of all the popes are stored. The contents inside were never intended to be kept secret.

That said, it’s not like just anyone can waltz in and take a peek around. The archives, which were founded in 1612, were completely closed to the public until 1881, when Pope Leo XIII began allowing Catholic scholars to conduct studies amongst the stacks. In recent years, the restrictions on researchers have been relaxed—slightly—but still remain pretty stringent. Only carefully accredited scholars are allowed to enter—journalists, students, and amateur historians are barred. And even if you meet the requirements to view texts from the Archives, no browsing is allowed. Scholars can request up to three folders a day—which can end up being a bit of a gamble, because not everything is cataloged, and some catalogs are written in Italian or Latin.

Three years ago, however, the Vatican decided to the celebrate the Archive's 400th anniversary by making 100 items available for public viewing for the first time at the Capitoline Museums in Rome. Of course, with 50 miles of shelving and documents dating back to the eighth century, 100 items only scratches the surface. But without unique access—or a plane ticket to Rome—those 100 documents, and any others that have been sourced by scholars, are all we can know of the "Secret Archives." Here are some of the highlights.

1. The papal bull from Pope Leo X excommunicating Martin Luther

On January 3, 1521, Pope Leo X issued the papal bull Decet Romanum Pontificem, which excommunicated Luther, thereby launching the Reformation. The earlier papal-issued Exsurge Domine had given Luther 60 days to recant his condemnation of the Church as outlined in his 95 Theses. Luther responded by burning his copy.

2. A 1530 petition from 81 English clergymen and lords asking Pope Clement VII to annul King Henry VIII’s marriage to Catherine of Aragon

In 1530, an heirless Henry was eager to marry Anne Boleyn—but divorce was not permitted within the Catholic Church. Despite the 3-foot-wide letter signed by 81 Members of Parliament and clergy (including the Archbishop of Canterbury), and threatening language that warned that "a refusal of annulment would require recourse to extreme measures for the good of the kingdom which we would not hesitate to take," Clement refused, resulting in the formation of The Church of England. Many of the seals of the signatories were affixed to the petition with a red ribbon, a practice that is sometimes considered the source of the term “red tape.”

3. Transcripts from the trial of the Knights Templar

After enjoying centuries of wealth and privilege as an elite army during the Crusades, the Knights Templar's prestigious status came to be seen as a liability. In what was likely an effort to avoid his financial debt to the order, Philip IV of France had all the knights arrested on October 13, 1307 and charged with heresy. After years of torture, many admitted to the trumped-up charges and were eventually burned at the stake. Pope Clement ultimately disbanded the Order under intense pressure from Philip. In 2007, the 60-meter-long document that comprises the minutes from the years-long trials was finally made public—revealing that the pope had first intended to pardon the Knights Templar before he was coerced into condemning them.

4. Correspondence relating to the trial of Galileo

Although by the 1600s, scientists were starting to question whether the Earth was really the center of the universe, the Church maintained that it was and persecuted anyone who publicly said otherwise. Physicist and astronomer Galileo Galilei had already been reprimanded for his beliefs in 1616, but had successfully defended himself by claiming that he had simply discussed the idea of a heliocentric universe without necessarily believing it. That argument failed to hold up in 1633, when the investigation under Pope Urban VIII found Galileo "vehemently suspected by this Holy Office of heresy, that is, of having believed and held the doctrine (which is false and contrary to the Holy and Divine Scriptures) that the sun is the center of the world, and that it does not move from east to west, and that the earth does move, and is not the center of the world."

5. and 6. Letters to Pope Pius IX from Abraham Lincoln and from Jefferson Davis

Both were written in 1863, at the height of the American Civil War. In his request that the Pope accept Rufus King as the U.S. representative to the Vatican, Lincoln made no mention of the violence tearing his country apart. Confederate President Davis, on the other hand, detailed the horrors of "the war now waged by the government of the United States against the states and people over which I have been chosen to preside." Jefferson's not-so-subtle angling to have the South recognized as an independent country by the Vatican failed, but only just. In a separate correspondence, the Pope addressed Davis as the President of the Confederate States of America, while Robert E. Lee believed that Pius was the only world leader who recognized the Confederacy.

7. A letter from Michelangelo to Pope Julius II

The letter warned the Pope that the Vatican guards hadn't received their paychecks in three months, and were threatening to walk off the job. It's not clear what ended up happening (or not happening) as a result of the artist's warning.

8. The Papal Bull from Pope Alexander VI splitting the New World

On May 4, 1493—just a year after Christopher Columbus "discovered" the New World—Pope Alexander VI issued the Inter Caetera, which gave Spain control over all new lands 100 leagues away from the Azores and Cape Verde. Effectively, this meant that the eastern part of present-day Brazil would be Portuguese, and the rest of the New World would be Spanish.

9. The doctrine of the Immaculate Conception

On December 8, 1854, Pope Pius IX issued the Ineffabilis Deus, officially committing to Apostolic Constitution the belief that Mary was conceived without "original sin."

10. A letter from Mary, Queen of Scots, a few months before her execution

Imprisoned for nearly two decades in England (she fled there after a Scottish revolt, hoping Elizabeth would protect her), Mary, believed to be a threat to the throne, was executed on February 8, 1587. Just a few months before her death, Mary wrote to Pope Sixtus V from her prison cell at Fotheringhay Castle in Northamptonshire, begging him to save her life and professing her Catholic faith, while also railing against her treatment and the alleged illegitimacy of the tribunal that condemned her.

11. A document from 809 CE

The oldest loose parchment kept in the entire archives dates from 809 CE and records part of a donation to a church in Venice.

12. A letter from Clement XII to the deputy of the seventh Dalai Lama

In it, the pope requests protection for a Franciscan mission in Tibet and freedom for the friars to preach the Gospel.

13. The design of a flying machine invented by a Brazilian priest

Wikimedia Commons

Bartolomeu Lourenço de Gusmão, a priest who lived in the then-Portuguese colony of Brazil in the late 1600s and early 1700s, spent his life studying how disparities in density should allow certain objects to float through the air. He made several demonstrations at the court of King John V of Portugal and designed plans for a never-completed flying machine, called the Passarola, which resembled a giant inflated bird.

14. A papal bull issued by Pope Innocent III calling for a new crusade to the Holy Land

Issued in 1198, this effectively launched the Fourth Crusade, which saw the capture of Constantinople by the Crusaders. Although the pope had originally sanctioned the Crusade, the sack of the massive city was so brutal he condemned it as "an example of affliction and the works of Hell."

15. A letter from China's Grand Empress Dowager Helena Wang to Pope Innocent X

Written on a silk scroll, the letter from the Empress, who had converted to Catholicism, appealed to the pope for help after the Qing Dynasty forced the Empress to flee Zhaoqing. Unfortunately, the letter never reached Pope Innocent X—he died before the messenger was able to gain an audience.

All photos courtesy of Getty unless otherwise noted