Heavyweight champion Muhammad Ali (right) and former champ Rocky Marciano (left) box in a composited film that was created in 1969 and released in 1970.

On the morning of his 1967 fight against Ernie Terrell in the Houston Astrodome, Muhammad Ali sat in his hotel room watching a film of Rocky Marciano challenging Jersey Joe Walcott for the heavyweight title 15 years earlier. Ali leaned forward, his head cradled in his hands, watching intently until a bloodied and trailing Marciano knocked Walcott out in the 13th round with a short, emphatic right. Then Ali turned to his manager, Angelo Dundee.

“Angelo, the man’s tough,” said Ali, according to reporting by Sports Illustrated. “He’d be hell to fight. I’d wear him at the end of my glove for 10 rounds but he’d still be coming. Meanwhile, I’d be tired — maybe too tired to dance — and Rocky would be throwing punches … that wouldn’t be no fight — that would be a war.”

Marciano was already the heavyweight champ in 1954 when a 12-year-old Ali took up boxing after having his bicycle stolen. At night, the boy would listen to his transistor radio in Louisville, Kentucky, and hear Don Dunphy’s staticky voice from faraway Madison Square Garden, announcing Marciano as the heavyweight champ-eee-on of the world.

In 1969, two years after Ali beat Terrell, the champ found himself in the ring with Marciano in one of the more bizarre fights in the annals of boxing. Ali was 27 years old and 29-0. Marciano was 45 years old and had retired 13 years earlier with a perfect 49-0 record, including 43 wins by knockout — history’s only unbeaten heavyweight champ.

The “Super Fight,” as it was billed, was fake, the concoction of a Miami promoter and disc jockey, Murray Woroner. If computers could help put a man on the moon, why couldn’t they predict the outcome of a match between two unbeaten champions from different eras? Woroner fed the fighters’ statistics into a computer, which spit out a script of different fight scenarios that Ali and Marciano were paid to reenact in a film studio in North Miami. The resulting film was edited and shown in movie theaters across the country and overseas, the outcome kept a closely guarded secret, even to the fighters.

Ali and Marciano seemed like polar opposites, the Great White Hope from the ’50s and the Angry Black Man from the ’60s.

Marciano had been a quiet conformist during his career, suppressing his anger toward a manager who stole from him and the Mafia that secretly controlled his career, along with most of professional boxing. He had served in the Army during World War II and became a symbol of American might during the Cold War, with a punch his manager compared to the atomic bomb.

Ali and Marciano seemed like polar opposites, the Great White Hope from the ’50s and the Angry Black Man from the ’60s.

At the time, Ali was one of the most hated men in America, not the folk hero he would later become. During his pummeling of Terrell in 1967, he had screamed at him, “What’s my name?” because Terrell had called him by his former “slave name” of Cassius Clay, as did most sportswriters. He hadn’t fought in more than two years and was locked in a battle with the federal government after refusing to fight in Vietnam, famously declaring, “I ain’t got no quarrel with them Viet Cong.”

If this fight film was made possible by the new age of technology, promoters played up racial and ethnic stereotypes that had always characterized boxing to hype the gate. Newspapers frequently carried stories that Marciano was considering coming out of retirement, including one report shortly after Ali took the title that a wealthy Texan had offered Marciano $4 million ($34 million today) to silence the loudmouthed young champ.

Shortly before Ali and Marciano met in Miami that summer, a federal judge had ordered Ali to serve five years in prison for refusing induction into the U.S. Army. He remained free on appeal, and in desperate need of funds. “I was in the deep freeze part of my exile, and there was no thaw in sight,” he wrote in his 1975 autobiography, The Greatest.

Marciano, who had let himself go in retirement, had gone back into training, lost 50 pounds and donned a toupee to mask his receding hairline. At 5 feet, 10 inches, he was dwarfed by the 6-foot-3 Ali, who was 20 pounds heavier. But Ali, who hadn’t fought in two years, looked flabbier. (I was able to recreate those sessions by interviewing two people who were there: Peter Marciano, Rocky’s brother, and Ali’s then-wife Belinda, now Khalilah Ali. I also found, in the archives of Sports Illustrated, a lengthy memo from a Time reporter who had interviewed other eyewitnesses at the time of the film’s release.)

Over the course of filming, the two champs sparred more than 70 one-minute rounds. They acknowledged that it was just playacting. They never clinched and seldom went for the head. But sometimes things got real. Ali would flick his lightning-quick jabs in Marciano’s face, prompting him to walk back to his corner muttering, “My God, the kid is so fast.” Ali delighted in flicking Marciano’s toupee off. An angry Marciano trapped Ali in a corner and pounded on his arms, then smashed a right to his solar plexus. “Ooof,” Ali exhaled, sinking to his stool. The taping stopped. Ali refused to continue until the promoter sent a driver to the bank to bring him another $2,000. One night they went out to dinner and ran into comedian Henny Youngman, who came over to their table and joked around. Ali’s arms were so sore that he had trouble lifting the saltshaker.

Staging knockdowns was tricky. Each man had been knocked down only twice in his career, and had to be coaxed to take a dive for the cameras. During one take, Ali shouted, “Drop the Wop” and hit Marciano, who fell to the canvas, took out his mouthpiece and roared with laughter. When it was Marciano’s turn, he teased a reluctant Ali by parodying him: “The onliest way I can be beat by any man is to knock me out.”

During a break one day, the conversation turned to the country’s racial divide and the riots that had swept the country. They sat on the floor next to the ring, sharing a bag of grapefruit. Ali would tear off a section and pass it to Marciano.

“Wouldn’t it be great if there was something we could do, me and you together, a white guy and a black guy?” said Marciano.

They talked about doing a bus tour of inner-city neighborhoods. Ali got excited.

“Imagine, Muhammad Ali and Rocky Marciano, going into the worst areas,” he said. “We could shake up the world, you and me. Would you do it? Would you do it?”

Marciano said he would. He encouraged Ali to hang tough in his fight with the Army. Marciano had a secret about his own struggle with the Army that he never shared with Ali but which I unearthed from old Army records. His patriotic image as a soldier who served in World War II concealed the fact that he and another GI had been court-martialed for robbing and assaulting two British civilians shortly before D-Day. He never deployed to Normandy but instead served two years as a military prisoner.

Marciano had never been comfortable with authority, nor with the mantle of Great White Hope. He forged close relationships with black fighters, including his boyhood idol, Joe Louis. (He cried after knocking out Louis in Madison Square Garden to end Louis’ career and advance his own.) Marciano told Ali about his Italian-American family’s struggles after settling in the shoe factory town of Brockton, Massachusetts. Sacco and Vanzetti, Italian anarchists and laborers, had been arrested on the Brockton trolley and executed in 1927, when Rocky was 3 years old, for a robbery and murder they didn’t commit. Politicians called Italians “a race of pickpockets” and “unfit foreigners.” Congress banned immigrants from Southern and Eastern Europe.

“People fear change,” Marciano told Ali.

The Ali-Marciano bus tour never happened. A few weeks after they parted, on Aug. 31, Marciano climbed into a Cessna in Chicago, bound for Des Moines, Iowa, and a party at a steakhouse owned by the nephew of a mob pal. The plane crashed in a cornfield in Iowa, killing everyone on board. Ali cried when he heard the news.

The following winter, The Super Fight aired in more than 600 theaters across America. Woroner had filmed seven different endings. In the first screening, a bloodied Marciano, trailing on points, knocked out Ali in the 13th round. Later, when the film was shown in Europe, Ali won. The fight looks phony. There are no spectators, just an eerie darkness surrounding the ring, with the sound of piped-in crowd noise. It’s as if the two men have been abducted by aliens and are fighting on a spaceship in outer space.

“He was the onliest one that would’ve given me some trouble,” Ali said shortly after attending Marciano’s wake. Later, Ali said that he felt closer to Marciano during their sparring sessions than he ever did to any other white fighter.

“Our work was phony,” he wrote in his autobiography. “But our friendship became real.”

Liner Notes This story has been changed to correct the number of times Muhammad Ali had been knocked down at this point in his career.