It is a tale that seems at home in an espionage thriller about ancient religious secrets, such as the "The Da Vinci Code."
For nearly 2,000 years, stories have circulated about the ultimate fate of sacred Jewish objects plundered from the Jerusalem Temple by Romans in A.D. 70—including a human-size, solid-gold Menorah. One widely shared theory among some Jews holds that the artifacts are hidden inside the Vatican, which many believe inherited the wealth of the Roman Empire.
There is only one problem, say many scholars: It isn't true.
Steven Fine, a Jewish history professor at Yeshiva University, has dedicated the past two decades to debunking these stories. This summer, he turned the question into the subject of his class on the Arch of Titus, an ancient monument still standing outside the Roman Forum that commemorates the capture of Jerusalem and depicts the Menorah being paraded through the streets of Rome in A.D. 71.
The assignment was prompted by a recent public flare-up: In late May, Mr. Fine spotted an open letter to then-Israeli President Shimon Peres. In it, Israeli Rabbi Yonatan Shtencel urged Mr. Peres to approach the Vatican and ask for the return of the Menorah, a cultural symbol so important it is pictured on Israel's state seal.
"I have a myth to kill," said Mr. Fine, speaking of the secret-Vatican-hoard theory. Mr. Fine is writing a book about the Menorah and its many legends, to be published next year by Harvard University Press. "If we don't nip it, it's going to get worse," he said.
In their own letter to Mr. Peres sent last month, Mr. Fine's students disputed each assertion in the rabbi's letter, after contacting his sources and consulting rare books. They haven't received a response from Mr. Peres, who left office this month, they said.
Rabbi Shtencel said he hadn't read the Yeshiva University response because it is in English, but said, "These aren't my claims. I am relying on several extremely serious sources."
Among them: Shimon Shetreet, a former Israeli minister of religious affairs, who said he raised the question of the artifacts during a meeting with Pope John Paul II in 1996 and separately with the Vatican's secretary of state, but got no answer. He wasn't surprised by that, he said, because "they are a very silent organization."
He said the issue wasn't raised when Mr. Peres traveled to the Vatican in early June.
"No one can dispute that they were taken to Rome," said Mr. Shetreet of the artifacts. "The question is what happened. It lies between legends, rumors and facts."
The Vatican dismissed accusations that it had the objects in a statement provided to The Wall Street Journal.
"I had heard once in the past rumors about such [a] story. But I never thought it was worthy of attention," said the Rev. Federico Lombardi, a Vatican spokesman. "It belongs to the genre 'mysteries of the Vatican,' in which some people exercise their fantasy."
Paolo Liverani, a professor at the University of Florence, said he received a handful of letters every year asking about the Menorah when he worked at the Vatican as a museum curator, but never came across the artifacts in the Vatican storerooms.
Still, he said, "it is very difficult to demonstrate things that don't exist."
Scholars say the myth surfaced in the U.S. during the 1950s and '60s, as the Vatican was working to improve relations with Jews in the wake of World War II. Additionally, they say troves of lost, buried Jewish treasures do exist—many hidden by Nazis.
"There's a whole world of subterranean manuscripts and antiquities," said Prof. Lawrence Schiffman, director of the Global Institute for Advanced Research in Jewish Studies at New York University. "A lot of that world is real."
But, he said, the Vatican theory isn't. "The story was created in the 20th century," Mr. Schiffman said. "There's no historical continuity."
Myths are also hard to uproot once they take hold, said Mr. Fine.
"People still feel pain," Mr. Fine said. "It's hard to get rid of that."
Some of Mr. Fine's students were initially wary of the class assignment. "At first I was almost afraid that this was anti-Jewish," said David Silber, a 21-year-old rising junior at Yeshiva. "But as we went further, the truth is the truth."
While the Arch of Titus and rabbinical sources depict the treasures in Rome in ancient times, that doesn't mean they ended up in storerooms of the Vatican, which was founded centuries later.
Some books Rabbi Shtencel cited in his letter weren't available in the U.S., so students had friends in Israel track down copies in university libraries there. Scouring the texts, they said they didn't find any eyewitness accounts of the temple artifacts inside the Vatican, as Rabbi Shtencel had claimed.
Their research didn't prove that the Vatican doesn't have the treasures. But "I'm convinced that his proofs are not valid proofs," Mr. Silber said.
There are many myths surrounding the fate of the Menorah, which is linked with the coming of the Messiah in Jewish lore, experts say. Some hold that it was stashed in a cave in Galilee, others that it lies submerged in silt under the Tiber River in Rome and still others that it is buried under a monastery in the West Bank.
Mr. Fine has his own theory: that it was taken by invaders who ravaged Rome in the fifth and sixth centuries and probably melted down.
"I say to people when I give lectures, 'Gold doesn't disappear. Maybe you're wearing the Menorah in your ring,'" he said. "That's a really unsatisfying answer for a lot of people."
—Joshua Mitnick contributed to this article.