With school children still learning "in 1492 Columbus sailed the ocean blue," and that he stumbled across North America by accident, it's no wonder Manuel DaSilva Rosa has a hard time convincing people the sailor was actually a Portuguese spy who knew exactly what he was doing.

Rosa, 48, does IT work for Duke University by day. But he has spent much of his extra time for 18 years, and some $80,000 of his own money researching this theory and penning a book on what he considers one of the biggest secrets ever kept.

"This cover-up was pretty well done," Rosa said of the 500-year-old story. "It was done at the state level."

The book, originally titled "The Columbus Mystery Revealed" when it was published in Portugal in 2006, was later published in Spain under the title, "Columbus: The Untold Story."

Rosa is currently working on an English-language edition he hopes to have published next year. Even after 18 years, he is constantly updating the story.

Ultimately, the tale goes something like this: Christopher Columbus was enmeshed with Portuguese royalty and agreed to be a spy for the throne by distracting Spain, its main rival, by "stumbling" across news lands.

These lands, known today as North America and the Caribbean Islands, were already known to the Portuguese to exist on the other side of the world from the East Indies thanks to the Vikings. At the time, the value of the trading routes to India outweighed the unknown potential of the Americas, so Columbus pretended to get lost on his way to India, knowing full well he was simply creating a diversion for the Spanish throne.

When asked how his obsession started (he's the first to admit it really has taken over his life) Rosa says it all began with disbelief.

In 1991, he was translating a manuscript on the subject from Portuguese to English and set off to disprove the thesis of the paper: that Columbus was a Portuguese spy who really knew where he was going. He says he is a "pit bull" when he sets his mind on something -- he cannot let it go until he's certain he knows the truth.

Rosa was born in the Azores, a cluster of Portuguese islands practically in the center of the Atlantic Ocean, where he and his five brothers lived without electricity or running water. His family moved to America when he was 12, but in both countries he was never taught that Columbus was connected to the Portuguese.

As far as he, and the rest of Portugal was concerned, he says, Columbus was not to be commended for getting lost on his way to the East Indies -- the strong navigational heritage celebrated by the Portuguese made Columbus less a hero and more a lucky idiot.

But hard as he tried, Rosa was unable to refute much of the evidence from the original manuscript, and has since uncovered more and more proof backing up that original thesis. Rosa says he has essentially traveled everywhere Columbus was known to visit, and he has dug up primary sources in the form of birth certificates, marriage licenses, and other documents that reinforce the notion that Columbus was a Portuguese spy.

"I just felt cheated," Rosa said after accepting the idea that Columbus was indeed sailing for Portugal. "The most famous navigator in the world was married to a Portuguese woman" and no one ever mentioned that.

Also, it is thought that Columbus was supposedly a wool weaver -- so why would anyone trust this man with a ship? Rosa points to a complicated navigational chart, thought to be hand-drawn by Columbus himself.

"The guy who drew this chart was very knowledgeable. He didn't spend the first 25 years of his life behind the wheel of a weaving machine," Rosa said. "He was not lost one day in his voyage."

Rosa says his research has been met with much skepticism, but that doesn't surprise him.

"Historians who have been fed the wool weaver lie as if it was the gospel truth have a hard time thinking they could be wrong," he said. "I don't take it personally. ... I do wish they would at least read before judging my research."

He encourages those who challenge him to do so with solid proof. After all, he said, this whole voyage started for him in trying to disprove someone else.

As for the national holiday, he knows there is controversy about whether or not it is appropriate to celebrate the life of an explorer who is thought to have been quite cruel to the indigenous populations of the Americas, regardless of what country he was sailing for.

Rosa looks at the three-day weekend from the perspective of a historian, not a humanitarian. "He was conquering new lands for a crown," he said. "That's just how things were done."

"The holiday is important because it was the beginning of a new era," Rosa said.