Underneath a car park besides the Vatican Library are 52 miles of shelves housing rare documents, some dating back as early as the 8th century, in the tens of thousands – if not hundreds of thousands Nobody knows for sure how many there are

This is the Vatican Secret Archive Its contents are a mystery and closely guarded against the prying eyes of the outside world No-one but the curators can enter its massive vaults: even the Archives' owner, the Pope himself, may not be allowed inside What secrets does this ancient repository of power and knowledge hold? Founded in 1612, the Vatican Secret Archives have an incalculable range of documents and an immeasurable depth of knowledge stored within But getting access to those documents is not easy

No-one was allowed in the archive until 1881, when the first Catholic scholars were granted access to the reading room But to read a document you have to specifically request it, and no-one is allowed to browse the many miles of shelves to see what the archive contains 35,000 documents have been indexed in by the Archive, but this is just a fraction of the items the Vatican has And if you want to see these indexes, you need to have permission from the Archive, obtained by getting a written recommendation from an established academic In other words, the Vatican Archives have complete control over who exactly gets to go inside, and over what they see

In 2010, the Vatican published a book highlighting examples of the documents it stores: they include a 16th century request to annul Henry VIII's marriage and letters from Abraham Lincoln and Thomas Jefferson, each appealing for support in the American Civil War However, these precious records are only representative of the Archive if we take the Archives' word for it: we simply have no objective confirmation that the Vatican possesses nothing more than a collection of letters and charters The high level of secrecy surrounding the Archives has encouraged many conspiracy theorists over many years to speculate as to what is really hidden inside The most popular theory has found its way into Dan Brown novels: that is, the idea that among the millions of parchments stacked on the ancient shelves are the earliest records about Jesus Christ Specifically, conspiracy theorists believe that the Holy See is guarding contemporary accounts and portraits created when Jesus was alive, or at least soon after he died

According to theorists, the Vatican is hiding these documents in order to propagate their whitewashed depiction of Christ, and to hide the most controversial fact about Jesus: that he married Mary Magdalene, and father a child According to researchers Michael Baigent, Richard Leigh & Henry Lincoln, if Jesus did have a child, then his descendants would continue the holy bloodline, and this bloodline is what has become known as the Holy Grail Such a human relationship with Mary Magdalene could undermine the divinity of Jesus in many people's eyes, and thus undermine the Church's authority If this hotly debated theory is true, then the Vatican is sitting on a potentially explosive secret that could dismantle the Roman Catholic Church But conspiracy theorists claim the Vatican is hiding an even more sensational secret

Ufologists Cris Putnam and Thomas Horn suspect that the Papacy knows something about the existence of extra-terrestrial lifeforms Naturally, when alien sightings and reports of abductions first began, it was in the interest of the Church to refute the existence of extra-terrestrials So, with top secret, government-funded searches for aliens being carried out across the world, it seemed possible that the Church might be using its considerable resources to find evidence for alien life…and suppress it, by burying it deep in its Secret Archives However, in 2008 the Vatican announced that alien life might well exist The following year, it held a conference about how to deal with alien life should we ever make contact

Putnam and Horn believe that Pope Benedict's unexpected resignation in 2013 was related to pressure within the Vatican to reveal the UFO secrets the Pope holds in the archives Since Pope Francis was elected, many Catholics have suspected him of having a secret agenda to reveal something hidden in the Vatican Secret Archives Yet the simple truth is we don't know what is in the Archives The confidential documents could have world-changing significance, or they could be as harmless as the Vatican claims The Vatican Archivists point out that a lot of the suspicions surrounding the Archives' contents come from a misunderstanding of its name

In Latin, it is called Archivum Secretum Vaticanum, which has been directly translated into Vatican Secret Archives But in Latin, secretum doesn't mean 'secret' in the modern sense; it actually means 'personal', because the Archives are officially the personal property of the Pope More specifically, the Archives are full of the Popes' personal correspondence, like those letters from Abraham Lincoln and Thomas Jefferson All the Popes' letters are publicly available up until 1939; everything after that is still top secret Since UFO sightings properly began in the Second World War, it may be that the Vatican does have secret evidence concerning extra-terrestrial life

Or it may not For now, we can only take the Vatican at its word