2. The Cathars Did Not Possess The Holy Grail
The Grail legend that The Da Vinci Code is based on draws heavily from the book The Holy Blood and the Holy Grail, a 1982 novel that involves speculation about the Holy Grail in the region of southern France. One thing of particular interest to the authors was the mysterious heretical sect known as the Cathars. They had a castle on Montsegur, which was besieged in 1244 as part of the Crusades. Shortly before the Cathars surrendered, some of them escaped by being roped down the face of a sheer cliff, carrying with them a mysterious object.
The authors of The Holy Blood and the Holy Grail speculated that the object that they were carrying was a collection of documents regarding Jesus’ relationship with Mary Magdalene; in fact, their knowledge of this relationship formed the basis of the Cathar heresy. Dan Brown drew on this speculation in presenting Robert Langdon’s quest for the Holy Grail in The Da Vinci Code. However, the fact is that we have no idea what, if anything, was carried out of Montsegur that night.
Additionally, the substance of the Cathar heresy could not have been the supposed “truth” about the bloodline of Jesus. Why? The Cathars were Gnostics. As such, they believed that the material world was inherently evil and therefore could not have revered the man Jesus; instead, they thought His true nature to be entirely divine. They believed that marriage and procreation were, though necessary, evil. So no, they could not have based their belief system on the marriage of Jesus or set any stock on a belief about His bloodline.