<P> Scavone (1999, 2003) has argued that the "Grail" in origin referred to the Shroud of Turin . </P> <P> Psychologists Emma Jung and Marie - Louise von Franz used analytical psychology to interpret the Grail as a series of symbols in their book The Grail Legend . This expanded on interpretations by Carl Jung, which were later invoked by Joseph Campbell . </P> <P> In 2016, Goulven Peron suggested that the Holy Grail may reflect the horn of the river - god Achelous as described by Ovid in the Metamorphoses . </P> <P> The Grail later appeared in films; it debuted in a silent Parsifal . The Silver Chalice, a novel about the Grail by Thomas B. Costain, was made into a 1954 film . In The Light of Faith (1922), Lon Chaney attempted to steal the Grail . Lancelot du Lac (1974) was made by Robert Bresson . Monty Python and the Holy Grail (1975) (adapted in 2004 as the stage production Spamalot) was a comedic adaptation . John Boorman, in his film Excalibur, attempted to restore a more traditional heroic representation of an Arthurian tale, in which the Grail is revealed as a mystical means to revitalise Arthur and the barren land to which his depressive sickness is connected . Indiana Jones and the Last Crusade and The Fisher King are more recent and successful adaptations . </P>

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