~from CWN (I'm confused. I thought Dan Brown said it's in the Louvre.)
An Italian archaeologist, Alfredo Barbagallo, claims that the legendary Holy Grail is hidden in the catacombs under the 6th-century Roman basilica of St. Lawrence Outside the Walls.
Barbagallo believes that the Holy Grail-- the chalice used at the Last Supper-- is kept in a room that is now buried under the basilica. His claim is based on two years of studying medieval iconography inside the basilica. In the wake of Barbagallo’s claim, archeological authorities in Rome may give approval for the catacombs to be opened and examined.
According to tradition, Pope Sixtus II entrusted all the treasures of the Church to Lawrence, a deacon in Rome. Some accounts testify that the Holy Grail was among those treasures. St. Lawrence himself was martyred in 258, and the basilica was built on the spot of his death.