When Dan Brown's novel was released, it caused quite a stir amongst academics, clerics and religious followers and critics across the world. Some argued his theories were purely illogical, even heretical, while others said they only gave validity to ones that have existed for many centuries. His most controversial theory is his account of the Holy Grail, which he asserts is not a chalice, but a human being - namely, Mary Magdalene.
His story suggests that this truth was suppressed by the church in order to conceal the Sacred Feminine, an ancient principle dictating that God has both male and female elements - one that Jesus himself supposedly adhered to. He uses Leonardo Da Vinci's painting of the Last Supper as evidence of this fact.
However, this is not his only contentious claim: he also states that Jesus and Mary were married, and moreover, that they had a child, named Sarah, who would carry on the bloodline in secret, only to be known by a privileged few. This minority, called the Priory of Sion (who would later become the Knights Templar) carried this secret through history; encoded evidence of which can be found on some historic mounments, including the famed Rosslyn Chapel.
However, Brown was not the first to make such assertions. Learn more about Foucault's Pendulum, and its role as inspiration for the book.