Robert de Boron's Joseph d'Arimathie (c. 1191-1202) revolutionized the tradition by Christianizing the Grail as the cup of the Last Supper used by Joseph of Arimathea to catch Christ's blood at the Crucifixion. Wikipedia +2 However, Robert's innovation involves exclusively male keepers—Joseph, then his brother-in-law Bron (the "Rich Fisherman")—with no specific female Grail Bearer. Wikipedia +2
This absence is significant. Robert establishes the Christian reliquary tradition that would dominate later interpretations, but his lineage is patriarchal. The feminine bearer present in Chrétien and Wolfram disappears, replaced by male guardians. Blogger As one scholar notes, this may reflect Church Law (Decretum Gratiani, 1140 AD) forbidding women near the altar—the Grail's increasing identification with Eucharistic vessels made female bearers theologically problematic for orthodox Christianity.