Hugh Thomson has led many expeditions to Peru, as recounted in his book “The White Rock: An Exploration of the Inca Heartland.”

With many a jungle drum, this week sees the release and promotion of “The Lost City of Z.” An adaptation of the book by David Grann, the film proudly proclaims that it is “based on an incredible true story” in which British explorer Percival Fawcett (Charlie Hunnam) “journeys to the Amazon and discovers the traces of an ancient, advanced civilization.” He is portrayed as a romantic, wronged hero who battles for the truth — a quite bizarre distortion of the facts.

The exploration of the Amazon has been one of the epic undertakings of the past few centuries. It has seen many heroic figures. But Fawcett was not one of them.

You will search the anthologies of exploration in vain for a mention of his name. He is not listed for one simple reason: He never discovered anything. In fact, later explorers like me have found him something of an embarrassment. He was a fantasist who happened to have a knack for publicity and a racist whose dim view of Amazonian cultures is probably what caused his demise.

As a boy, I had a copy of “Exploration Fawcett,” a posthumous collection of his writings. The cover illustration, drawn by Fawcett, shows an anaconda as long as a canoe menacing the intrepid explorers and their Indian helpers as Fawcett raises a gun to shoot it. “Hardly waiting to aim,” he recounts, he “smashed a .44 soft-nosed bullet into its spine, ten feet below the wicked head.”

Those who’ve traveled on the Amazon know that it is in reality mundane, soporific and almost dreamlike. Very little happens, slowly. It is perfectly possible to travel for days without seeing any wildlife, let alone an anaconda, which would slither away at the sound of oncoming canoes.

Fawcett self-mythologized, presenting jungle journeys as if they were Homeric odysseys. He was inspired in his descriptions by adventure novels such as Jules Verne’s “La Jangada” and the works of Rider Haggard. All featured trusty companions, unreliable natives and clues given by some ancient chronicle.

The relationship between Edwardian writers and explorers was a symbiotic one. Arthur Conan Doyle knew Fawcett well (they shared an interest in spiritualism), and he based “The Lost World” on some of Fawcett’s accounts — accounts that gave the world a version of Amazon exploration that it could recognize from fiction.

Fawcett’s sponsors at the Royal Geographical Society lapped it up, as Hollywood has now. The movie presents a cartoon version of the Amazon, where human heads line the entrance to an Indian camp.

When Fawcett disappeared in Brazil in 1925, along with his 21-year-old son and another companion, it caused a public outcry and a journalistic sensation. A series of privately funded expeditions were mounted to find him. Occasional sightings of a lone white man somewhere in the jungle — even if thousands of miles from where Fawcett was last seen — were enough of an excuse for editors of the day to raise the story again.

What most likely happened to Fawcett, although not something you will learn from the movie, has been painstakingly re-created by distinguished Amazon historian John Hemming, in his 2003 book “Die If You Must,” and documentary-maker Adrian Cowell, in his 1960 book “The Heart of the Forest.”

Hemming has documented Fawcett’s “ugly racist notions about the Native Americans.” Fawcett described one tribe he encountered as “large, hairy men, with exceptionally long arms, and with forehead sloping back from pronounced eye ridges — men of a very primitive kind; villainous savages; great apelike brutes who looked as if they had scarcely evolved beyond the level of beasts.” In this he was nothing like the movie character, who stands up for the Indians he encounters, delivering a passionate speech in their defense at the Royal Geographical Society, while all around him less-enlightened old codgers proclaim their savagery.

As Grann acknowledges in his book — again, you will find nothing of it in the film — Fawcett was deeply conflicted about his suspicion that there might have been an earlier advanced civilization in the Amazon (a suspicion that, for all the wrong reasons, he was right about, although he himself never found anything to prove it). He could not reconcile this with his poor opinion of the Indian tribes, so he postulated the existence of “white Indians” who had somehow traveled across the Atlantic from Europe and brought civilization with them.

It seems that Fawcett’s dismissive attitude toward the Indians, not his bravery, landed him in situations that risked his life and that of his son. He recognized that tribes could be naturally hospitable, but he failed to recognize that they expected any visitors to be equally liberal.

Expeditions to the Amazon, then and now, would always bring gifts. Fawcett did not, while still availing himself of anything the Indians could give him. Moreover, George Dyott, the leader of one of the expeditions sent to find him, was told by Indians that Fawcett had broken an unwritten rule of forest travel. He had seen two canoes on a riverbank and simply taken them. Naturally, the Nahukwá, whose canoes had been stolen, did not react well.

Likewise, when Fawcett shot a duck — and much is made in the movie of his prowess as a marksman — he refused to share it with his Indian helpers. He also struck a young Indian boy who was playing with his knife. As Hemming remarks: “Striking an Indian in anger is a deep insult. The Xingu Indians are infuriated by any aggression against a child, since they are deeply affectionate parents. . . . And native hunters invariably share out their game.”

The Villas-Bôas brothers — Brazilian anthropologists legendary in Amazonia for their longtime work protecting the Indians — have commented that “Fawcett was the victim, as anyone else would have been, of the harshness and lack of tact that all recognized in him.”

Grann’s book captures some of this — it is intelligent and nuanced, as one might expect from a New Yorker staff writer. But it is also a source of distortion, as it ignores or inflates much available material on Fawcett.

Hemming, whom Grann consulted and thanks in the book, wrote in a review for the Times Literary Supplement that Grann had been seduced by the “jungle as green hell” genre of travel writing, with fanciful pages about ferocious piranhas, huge anacondas and even cyanide-squirting millipedes. Whereas Grann suggests that as many as 100 people lost their lives in search of Fawcett, Hemming corrects the record: One person died. “It is a pity that a writer as good as Grann chose to study this unimportant, disagreeable and ultimately pathetic man,” Hemming concludes. “It is an even greater pity that he decided to inflate and distort so much of this sad story.”

To be fair, Grann presents some of Fawcett’s more far-fetched claims much like the antics of a carnival artist. So what if the guy says he’s the strongest man in the world? Unfortunately, the movie accepts Fawcett’s claims at face value. The compulsion to make Fawcett a hero has won out over the far more interesting aspects of the story. James Gray, the film’s director and screenwriter, has chosen to portray him in an unrecognizable way: as a sober and serious underdog taking on the establishment, rather than as the blundering and racist flake that he clearly was.

If the filmmakers had been looking for a real hero to make a movie about, they could have found one much closer to home. Around the same time Fawcett was getting lost in the jungle, American explorer Hiram Bingham made some genuine and extraordinary discoveries of Inca ruins — Machu Picchu being just the most famous. He was also an academic at Yale who had, unlike Fawcett, made scrupulous studies of the historical material and was deeply sympathetic to the Indian population. Standing well over six feet tall in his fedora and knee-length boots, it is he, not Fawcett, who was the original swashbuckling model for Indiana Jones. Later in life, he married a Tiffany heiress, had seven sons and became a senator before being censured. Plenty for Hollywood to get its teeth into.

When I started leading expeditions to the Peruvian Andes in the 1980s, I went to Hemming for advice, and he told me something I’ve never forgotten: “While anyone might be able to find a ruin in South America, it can take a lifetime to understand what it means.”

For the process of exploration should be as much an intellectual one as a physical one. Fawcett was a serving army officer and, as such, was good at the business of surveying the disputed border territories of Brazil and Bolivia. But he knew nothing of archaeology and anthropology, and so when it came to his wild goose chases after scraps of unreliable evidence and his theorizing about the existence of early civilizations, he was way out of his depth.

In a curious way, the willful ignorance of this film echoes the willful ignorance of Fawcett himself. Why stick to the facts when you can play to a myth? But even if truth may sometimes be stranger than fiction, that is not a licence to invent it. For this is indeed an incredible story. Just not a true one.