For at least some of his claims (e.g. the idea that Jesus and Mary Magdalene were married and/or had a romantic or sexual relationship), Brown is able to cite some ancient texts that (if interpreted in the tendentious way he is suggesting) can be seen as supporting them.  He has his quotes from the gospel of Philip and the gospel of Mary.  But with respect to the “greatest cover-up in human history” Brown is not able to cite a single ancient text that even hints at it.  That’s because there are none.