The Vatican has for the first time opened up its Secret Archives to an outside publisher, allowing the treasures held in its 85 kilometres of shelving to be photographed.

The 800-year-old archives were originally held in Castel Sant’Angelo before being transferred to Vatican City. Monsignor Sergio Pagano, the Prefect of the Secret Archives, said they exercised “a special fascination” because the priceless documents they contain chronicle “a long and incomparable history which stretches back to the very roots of the Church of Rome”.

They also arouse a sense of mystery and imagination because access to the archive is strictly limited. As Cardinal Raffaele Farina, archivist and librarian of the Holy Roman Church, puts it, “popular books and films” love to imply there are “deep dark secrets intentionally hidden from public view”.

Only scholars who offer cast-iron credentials and a convincing reason for wanting to consult the archives are allowed to enter — and even they are confined to a reading room to which the documents are brought from the hidden stacks by Vatican archivists.

However, Paul Van den Heuvel, a Belgian publisher, was given permission to wander through the stacks and shelving in the frescoed Tower of the Winds inside Vatican City, and recently took a group of journalists with him.

We watched Enrico Flaiani, a Vatican archivist, don white gloves to turn the pages of two of the countless historical documents: the 1521 Edict of Worms excommunicating Martin Luther, and the 1797 peace treaty of Tolentino between the French Republic and the Holy See.

The oldest treasure is the Liber Diurnus Romanorum Pontificum, a book of legal formulas used in the papal chancellery, which dates to the end of the 8th or beginning of the 9th century. There are papal letters ranging from Clement VII’s 1530 letter to Emperor Charles V on his coronation to a letter to Adolf Hitler from Pope Pius XI in 1934 on the “obstacles” to good relations between the Holy See and the emerging Nazi Germany, as well as letters by St Teresa of Avila, St John Bosco, Erasmus of Rotterdam, Voltaire and Michelangelo.

Other highlights include the 12th-century Concordat of Worms between Pope Calixtus II and Emperor Henry V; a 13th-century guarantee of safe conduct issued by the Khan of Persia to a papal embassy returning to the West; and the 1294 letter from the College of Cardinals to the Abruzzo mountain hermit Pietro Morrone appointing him as Pope Celestine V (he did not last long, becoming the only Pope in history to step down voluntarily, in 1296).

Then there is the record of the 14th-century trial of the Knights Templar; a 1494 letter from Lucrezia Borgia to her father, Pope Alexander VI, warning him of plots against the Borgias by the Sforza and Colonna families; the enrolment of the first contingent of the Swiss Guards in 1505; and the (unsuccessful) petition by English peers and bishops to Clement VII in 1530 asking him to dissolve Henry VIII’s marriage to Catherine of Aragon — it went missing in the 19th century and was rediscovered under a chair in 1926.

The upheavals of the Reformation are also reflected in a poignant letter from Mary, Queen of Scots, to Pope Sixtus V in 1586 affirming her innocence and her Catholic faith shortly before her execution, while the spectre of the Inquisition haunts the records of the trial of the great astronomer Galileo Galilei for heresy between 1616 and 1633.

From more recent times the shelves yield the dogma of the Immaculate Conception of the Virgin Mary in 1854; letters in 1863 to Pius IX from Abraham Lincoln, President of the Union, and Jefferson Davis, President of the Confederate States, on the American Civil War; the scripts of Pius XI’s radio messages of 1938 on the gathering clouds of the Second World War, with corrections in his own hand; the dogma of the Assumption of the Virgin Mary in 1950; and Pier Luigi Nervi’s designs for the Paul VI audience hall in the 1960s.

Some of the documents have additional rarity value because of the material on which they were written, including the 10th-century “diploma” of Emperor Otto I, an agreement between the Saxon King and Pope John XII (formerly Octavian, son of the powerful Prince Alberic II, the ruler of Rome) on purple parchment with gold ink, and a letter from a Native American to Pope Leo XIII in 1887 on birch bark, addressing him as “the Great Master of Prayer, he who holds the place of Jesus”.

Unlike countries that allow archives to be opened after a time limit, the Vatican opens up its records one pontificate at a time, the last being that of Pope Pius XI, who died in 1939. With the exception of documents relating to the Second Vatican Council in the 1960s, most of the archives after 1939 remain for the time being inaccessible — most controversially, material relating to Pius XII’s alleged silence over the Nazi persecution of the Jews.

However, the new book, says Cardinal Farina, will go some way to dispelling the aura of mystery surrounding the archives. The volume costs €50 (£45) — and for collectors there are 50 copies with linen binding at €299 and 33 copies (one reserved for the Pope) of a special edition in sheep parchment for €4,950.

Those who have seen the film of Dan Brown’s Angels and Demons, in which a document by Galileo provides the clue to the mystery, will be disappointed to learn that there is no glass-enclosed lift descending into a sealed low-air pressure chamber, and no series of complex security systems. Instead a series of stairs leads from the a two-storey underground bunker to the top, which houses a former observatory and offers a spectacular view over Rome.

The steel doors into the archives are impressive, however, and the seemingly endless stacks are temperature controlled. I asked Dr Flaiani whether anyone had managed to steal a volume or tear a leaf from a document, as occurred in the film.

“No, but we have had a case of the opposite,” Flaiani said.

The opposite?

“Someone trying to prove that they had aristocratic lineage once inserted pages into a Vatican document on genealogy, and then tried to use this as evidence that they were entitled to the family estates.”

Did it work? Flaiani smiled. “No, the ruse was discovered,” he said. “We are very vigilant.”