SALEM, N.H. -- Dennis Stone looks at the 9-foot-long, 4 1/2-ton slab of granite on a hilltop here in southern New Hampshire, and sees a 4,000-year-old sacrificial altar built by the ancient Phoenicians to honor their gods. He sees an ancient locus of magic and mystery, birth and death.
Ken Feder, a professor of anthropology at Central Connecticut State University who has studied the 20-acre site, looks at the slab and sees a place to make soap.
''It's a lye stone," Feder said. ''About 300 years old."
After the bestseller ''The Da Vinci Code," Stone's version of history is finding a receptive audience. About 75 percent of people who come to ''America's Stonehenge" walk away believing that the rocks and caves are an ancient religious site.
''People were more skeptical in the '70s," Stone said. ''They're more open-minded now."
Tales of Europeans who lived in the Americas hundreds -- even thousands -- of years before Columbus have been around for decades.
But with the advent of ''The Da Vinci Code," they are finding an ever-broader audience.
The book, which has sold about 50 million copies, and which opened as a movie last week, tells the fictional tale of a massive, eons-old church coverup.
The weaving of fact and fiction by the book's author, Dan Brown, has fueled an array of conspiracy theories that there may be other subverted historical truths waiting to be discovered.
In Westford, Mass., at the site where a Scottish knight was supposedly buried a century before Columbus discovered America, historians and researchers say they have received hundreds of inquiries from around the world since the book was released.
And Stone, whose father bought the property on which sits ''America's Stonehenge," says business so far this year has been great.
The wax and wane of these alternative theories of the country's past have come in spurts for hundreds of years.
Thomas Jefferson, the third president and himself an amateur archaeologist, was obsessed with uncovering a majestic history of North America after European intellectuals had routinely snubbed the New World as a wasteland only recently raised from the swamp.
A century later, Joseph Smith, founder of the Church of Jesus Christ of Latter-Day Saints, the Mormons -- which now has 12 million adherents -- preached that the Americas were populated by a people who had come from the Middle East at about 2,200 BC.
And in the 1970s, Barry Fell, a Harvard University marine biologist, wrote several books outlining his belief that North America was inhabited by Libyan, Phoenician, and Celtic traders dating back thousands of years.
''America was like a crossing ground for all these cultures," Stone said.
Academics such as Feder say the ideas are fanciful -- but impossible to disprove. Stories of exotic cultures sacrificing human beings on New Hampshire hilltops are far more interesting than the more mundane reality of a Colonial farmer trying to stay clean.
In ''The Da Vinci Code," Brown writes about how the offspring of Mary Magdalene and Jesus were protected from the church by a fraternity called the Knights Templar. The Knights did exist, and they were persecuted by the church.
''What Brown did was mix up a lot of stories and medieval folklore and urban legends with some history, and it caught fire," said Dan Burstein, who is author of ''Secrets of the Code," a book that analyzes the stories in ''The Da Vinci Code."
''It already was resonant, and this just amplified everything," Burstein said.
The story of the Westford Knight has been around for at least 60 years and has been the focus of at least four books since ''The Da Vinci Code" was published, said Elizabeth Lane.
Lane has researched the subject, and has helped to archive the history in Westford.
According to the legend, the knights left Scotland looking for a safe haven. They ended up exploring the coast of New England, ultimately sailing up the Merrimack River where, in 1398, a group of them climbed the highest hill around to get their bearings.
There, one of them died and was buried. An armorer punched his likeness into the rock nearby as a memorial.
That image, though not clear, can be discerned today. But whether it involves glacial striations, an artist's work of fancy, or the likeness of a 14th century adventurer, is a matter of debate.
Archaeologists have dismissed the story, but the legend has grown since ''The Da Vinci Code" came out, Lane said. In the past four years, she has received inquiries from around the world.
In Salem, meanwhile, Stone pulls together a broad spectrum of ideas to support his ideas of how ''America's Stonehenge" was formed. While unorthodox, the tale is convincing to many.
''I think its very possible that Europeans were here 10,000 years ago," said Dana Folley, of Raleigh, N.C., who was visiting the sites on Wednesday. ''Our view of history is always changing."
Among Stone's supporters are members of the New England Antiquities Research Association, an organization of amateur archaeologists that asserts that there are 800 sites around New England that were left behind from pre-Columbian visitors from Europe.
Mainstream archeologists say that the Americas were populated about 17,000 years ago, when nomads crossed a land bridge over what was is today the Bering Strait, which is between Alaska and Russia.
The archeologists generally believe that Europeans did not set foot in what is today the United States until the 15th century.
Stone sees things differently. On a 10-foot-high map on a wall in the visitors' center to ''America's Stonehenge," he has drawn the paths that he believes pre-Columbian visitors took from Europe and the Middle East.
Stephen Williams, who taught archaeology at Harvard for 37 years, groaned at the mention of the pre-Columbian visitors. Fifteen years ago, he wrote a book called ''Fantastic Archaeology" that attempted to debunk the notion of pre-Columbian Europeans in the United States.
''But this is a battle that has to be fought every 20 years," he said, likening it to the debate between evolutionists and creationists.
Among the curious who visit ''America's Stonehenge" are a number of Mormons. Latter-Day Saints are taught that two of the lost tribes of Israel lived in the Americas 2,000 years before Jesus.
''There is extensive evidence of communication between the old world and the new world for a long time before Columbus," said John Sorenson, an emeritus professor of anthropology at Brigham Young University in Utah.
Feder sees a problem with these theories. When other cultures come here, they leave things behind, he said. That's how legitimate theories gain traction.
''It's like ghost stories around a campfire," Feder said. ''They're fun to discuss, and maybe a small part of you wants to believe them, but they're just stories."
Douglas Belkin can be reached at email@example.com.