The Priory of Sion is a European-based secret society organized for the task of keeping safe the descendants of Jesus Christ and Mary Magdalene. The Priory is used fictitiously, but also has some basis in fact. Anti-Semitic Vichy sympathizer Pierre Plantard named his newly-created organization The Priory of Sion in 1956 and claimed he was the last heir to the French Merovingian dynasty.
Plantard's claim is based on Les Dossiers Secrets, which purportedly hold the link from the ancient Priory founded in 1099 by Crusaders in Jerusalem to the modern one he founded. Later, under oath, he admitted the Dossiers were fake. A theory popularized by Dan Brown in his book The Da Vinci Code postulates that the ancient Priory of Sion was said to be charged with protecting the bloodline of Christ: a historical secret the Catholic Church would go to extreme lengths to keep hidden. The Priory and the Dossiers on which it was based were later debunked as myth created by Plantard to assert his claim to being the prophesized Great Monarch.
Les Dossiers Secrets were used as the basis for the non-fiction book Holy Blood, Holy Grail. This book claimed as fact that the Priory of Sion is a secret society with Grand Masters such as Leonardo Da Vinci and Issac Newton, that the Knights Templar is its financial and military branch, and the Merovingian dynasty will once again rule when its descendants sit on the thrones of Europe.