From Wikipedia

Timewatch - The History of a Mystery

The Holy Blood and the Holy Grail (retitled Holy Blood, Holy Grail in the United States) is a controversial book by Michael Baigent, Richard Leigh, and Henry Lincoln.

The book was first published in 1982 by Jonathan Cape in London, as an unofficial follow-up to three BBC TV documentaries being part of the Chronicle series. A sequel to the book, called The Messianic Legacy, was published in 1987. The original work was reissued in an illustrated hardcover version in 2005. One of the books, according to the authors, which influenced the project was L’Or de Rennes (later re-published as Le Trésor Maudit), a 1967 book by Gérard de Sède, with the collaboration of Pierre Plantard.

In The Holy Blood and the Holy Grail, the authors put forward a hypothesis that the historical Jesus married Mary Magdalene, had one or more children, and that those children or their descendants emigrated to what is now southern France. Once there, they intermarried with the noble families that would eventually become the Merovingian dynasty, whose special claim to the throne of France is championed today by a secret society called the Priory of Sion. They concluded that the legendary Holy Grail is simultaneously the womb of saint Mary Magdalene and the sacred royal bloodline she gave birth to.

An international bestseller upon its release, The Holy Blood and the Holy Grail spurred interest in a number of ideas related to its central thesis. Response from professional historians and scholars from related fields was universally negative. They argued that the bulk of the claims, ancient mysteries, and conspiracy theories presented as facts are pseudohistorical. Nevertheless, these ideas were considered blasphemous enough for the book to be banned in some Roman Catholic-dominated countries such as the Philippines.

In a review of the book for The Observer, literary critic Anthony Burgess wrote: "It is typical of my unregenerable soul that I can only see this as a marvellous theme for a novel." Twenty-one years later, the theme of The Holy Blood and Holy Grail would be fictionalised by Dan Brown in his best-selling 2003 conspiracy fiction novel The Da Vinci Code, even using Richard Leigh's and Michael Baigent's last names (Baigent's scrambled) for the character Leigh Teabing.