Spoiler alert: If you have not read "The Da Vinci Code," and hope to be surprised by its revelations in the book or film, read no further. The secret is revealed here.

ATHENS, Greece — In "The Da Vinci Code," the Holy Grail is neither an object nor an objective. It symbolizes an earthshaking secret: Mary Magdalene bore a child with Jesus.

The mega-selling book — the film version of which opens tomorrow — is fiction. But, as grail legends go, it's in good company. The only undeniable truth about the grail is that there's no shortage of tales about it.

Since the Holy Grail became part of the popular Christian imagination in the Middle Ages, it's taken an array of forms. The most enduring grail image is of a vessel — perhaps a chalice — held by Christ at the Last Supper and later used to catch his blood during his final hours.

But the stories also soar off in many other directions. In some, the grail is a stone that fell from heaven and has mystical powers. Others have described it as a kind of Holy Spirit that bestows wisdom and revelation. Or it could be, some scholars suggest, nothing at all. The grail could simply be an artifact of language that's still familiar today: a metaphor for a quest in which only the most clever and steadfast can succeed.

In literature, the search for the grail has inspired imaginations for centuries, from the sagas of King Arthur to T.S. Eliot's "The Waste Land." In movies, it's been pursued by Indiana Jones and lampooned by the Monty Python troupe. Richard Wagner's last opera, "Parsifal," is based on the medieval story of a young Welsh knight who glimpses the grail in its guardian's castle. Some historians claim that Wagner's work so captivated Adolf Hitler that he set up an elite Nazi unit to try to find the grail.

"The important thing about the grail is its elusive quality," said Joseph Goering, a University of Toronto professor of medieval history whose 2005 book, "The Virgin and the Grail: Origins of a Legend," draws links to 12th-century paintings of Mary holding an enigmatic, radiant bowl. "The grail is always leading you on in some ways."

Many scholars contend the grail story borrowed elements of Celtic lore and other bits from the myths of antiquity. But it took on a distinctly Christian aura in France about 800 years ago when it became linked to St. Joseph of Arimathea, who was said to have received the vessel after the Last Supper and that it was used to catch Christ's blood during the crucifixion.

This has led linguistic detectives to theorize that "grail" comes from the old French word "graal," meaning dish or shallow platter. Yet even here there's another dispute. A few — in the vein of "The Da Vinci Code" — have suggested it comes from "sang real," or "royal blood" in French, as a reference to the bloodline of Christ and the deepest "secret" of the faith.

Such conspiracies have been given a boost in recent decades by scholarly attention to texts — including mystical Gnostic works and the recently publicized Gospel of Judas — that suggest alternative views to the books of the New Testament.

The idea of the grail quest — a centerpiece of the Camelot legends — was popularized by the French romantic poet Chretien de Troyes in the late 12th century. Such journeys came to represent the highest expressions of medieval chivalry, courtly romance and spiritual virtue.

In other words, an early literary fad was born. Across Europe, grail stories sprouted. They were given a boost by the Crusades and the belief that — somewhere out there — was the grail castle and other Christian visions such as Prester John, a monarch said to preside over a utopian Christian kingdom in the East.

But grail hunters didn't just head toward the Holy Land. The grail map includes such points as Scotland, Spain and France.

One of the most repeated legends again involves St. Joseph of Arimathea. The tale goes that Joseph was imprisoned after the resurrection, but smuggled the grail into his cell and that it miraculously sustained him with food and water. Upon his release, he takes a band of followers to Britain, along with the grail.

Stories over the centuries have placed the grail in the bowels of the 15th-century Rosslyn Chapel in Scotland — featured in the "The Da Vinci Code" — or Glastonbury Tor in Britain, which some contend is the mythical Avalon where King Arthur's spirit lives.