Dan Brown’s bestselling conspiratorial thriller The Da Vinci Code seems like ancient history now. At its peak of popularity, the novel set records both for sales and for irritating scholars with its view that Jesus and the 12 apostles held to gnostic heresies. The book’s bizarre plot focuses on Jesus’ bloodline extending through a child born by Mary Magdalene. Within that narrative, Brown asserts that the New Testament canon was determined by the Roman Emperor Constantine—who was not friendly to…