I figure it occurred before Julian.
Early Church fathers suppressed the Gospels of Peter, Thomas, and Judas. They did so because they didn’t care for the messages contained in those gospels.
Julian’s great oppression of Christianity was to forbid Christians from teaching the Iliad and Odyssey, just as Pagans were not permitted to teach the Gospel. Roman Pagans prefer to refer to Julian as “the Divine”.
Sure.
And Dan Brown knows more than anyone who has ever lived even Jesus Christ Himself and the Apostoles.