In 1956, a French draughtsman named Pierre Plantard officially registered a small low-income housing advocacy group called the Priory of Sion. Over the next two decades, Plantard transformed this mundane association into a grand esoteric fantasy. Desperate to prove he was the rightful Merovingian heir to the throne of France, Plantard created a series of sophisticated fake documents, genealogies, and forged medieval parchments with the help of his associate Philippe de Chérisey.
To give these fabrications historical legitimacy, Plantard secretly deposited them into the Bibliothèque nationale de France under various pseudonyms, calling them the Secret Files of Henri Lobineau. The documents claimed that an ancient secret order had protected the bloodline of Jesus Christ and Mary Magdalene for centuries. The hoax gained global traction when researchers used the forged files to write the 1982 bestseller The Holy Blood and the Holy Grail, which later became the foundation for Dan Brown's mega-hit novel The Da Vinci Code.
The entire delusion unraveled in 1993 when a French judicial investigation exposed Plantard's fabrications under oath, revealing that the mystical Priory was nothing more than a grandiose mid-century fraud.