The Prieuré de Sion, translated as Priory of Sion, was a fraternal organization founded in France in 1956 by Pierre Plantard in his failed attempt to create a prestigious neo-chivalric order. In the 1960s, Plantard began claiming that his self-styled order was the latest front for a secret society founded by crusading knight Godfrey of Bouillon, on Mount Zion in the Kingdom of Jerusalem in 1099, under the guise of the historical monastic order of the Abbey of Our Lady of Mount Zion. As a framework for his grandiose assertion of being both the Great Monarch prophesied by Nostradamus and a Merovingian pretender, Plantard further claimed the Priory of Sion was engaged in a centuries-long benevolent conspiracy to install a secret bloodline of the Merovingian dynasty on the thrones of France and the rest of Europe. To Plantard's surprise, all of his claims were fused with the notion of a Jesus bloodline and popularised by the authors of the 1982 speculative nonfiction book The Holy Blood and the Holy Grail, whose conclusions would later be borrowed by Dan Brown for his 2003 mystery thriller novel The Da Vinci Code.

The Holy Blood and the Holy Grail is a book by Michael Baigent, Richard Leigh, and Henry Lincoln.