ヴォルフラム・フォン・エッシェンバッハ
In "Parzival", Wolfram von Eschenbach, citing the authority of a certain (probably fictional) Kyot the Provençal, claimed the Grail was a Stone, the sanctuary of the neutral angels who took neither side during Lucifer's rebellion. It is called "Lapis exillis", which in alchemy is the name of the Philosopher's stone.