Tommie Smith, the 6' 3", 180-pound gold medallist, and John Carlos, the squat third-placed runner, stood shoeless on the presentation podium in the Mexico City stadium after the 200 metres final. Smith wore a black scarf around his neck and Carlos a string of Mardi Gras beads.

The athletes' clenched fists represented black power and their shoeless feet and black socks the grinding poverty in which many blacks lived. The scarf and beads symbolised the lynchings of blacks in America. Smith carried a box in his left hand containing an olive tree sapling, the emblem of peace. Their bowed heads expressed the belief that the words of freedom in the American national anthem only applied to Americans with white skin. Carlos told reporters: "White Americans will only give us credit for an Olympic victory. They'll say I'm an American, but if I did something bad, they'd say I was a negro."

Before the ceremony the two athletes had spoken in the changing-rooms. "Tommie, if anyone cocks a rifle," said Carlos, "you know the sound. Be ready to move."

Silver medallist Peter Norman overheard the conversation and Carlos asked him if he would participate. Norman, who would later be severely reprimanded by the Australian authorities, agreed and Carlos gave him a large Olympic Project for Human Rights badge. Norman pinned it to his tracksuit.

The athletes moved outside and stood to attention behind three young Mexican women, each of whom carried a velvet pillow with a medal placed on top. Irish International Olympic Committee (IOC) vice-president Lord Killanin and the president of the International Amateur Athletics Federation (IAAF), the Marquess of Exeter, led them to the medal ceremony.

"As Killanin hung the medal around my neck and shook my hand," said Smith, "his smile was so warm I was surprised. I smiled back. I saw peace in his eyes. That gave me two or three seconds to gather myself."

When the anthem began the three turned to the right to face the American flag. Smith and Carlos bowed their heads as if to pray and, tensing the muscles in their shoulders, prepared themselves. When the Star Spangled Banner began they raised their clenched fists into the thin air. At that moment, a blinding fury blew across right-wing, middle America. In that gesture, 30 years ago yesterday, the outcome of the 200 metres final became a mere footnote in Olympic history.

"I saw the race and I saw the salute," says Noel Carroll, an Irish competitor in the 400 and 800 metres in Mexico and a student at Villanova University at the time. "I recall it quite vividly. I was close to the black athletes while I was a student and I was aware that there was a mood of discontent within the sports world, particularly in basketball.

"Everyone had arrived in Mexico early for the Games because of the altitude and the Americans had been training before that up in Lake Tahoe, so there was fertile ground for agitation. The likes of Carlos and Smith were disciples of that movement. But when they made the clenched fist my impression was that there wasn't a great deal of local interest. There was no feeling that we were sitting through one of the greatest events in history and I didn't feel I was watching the most momentous moment of the decade.

"The gut feeling was that the lads (Carlos and Smith) had insulted the American flag, but kicking them out of the Games was an over-reaction by the officials. People felt that Brundage (Avery, IOC president) had overextended his power."

Smith and Carlos arguably made the most powerful non-violent protest sport has ever seen. Muhammad Ali quickly grasped the significance of the gesture. "It was the single most courageous act of this century," he said.

It was not the first time the Olympics had become enmeshed in the politics of race. Jessie Owens's five-medal haul at the 1936 Games - a showcase for the Nazi regime in Berlin - promoted the American sporting establishment as leaders in the struggle for human rights and racial equality.

Smith and Carlos had become immersed in the black power movement. When Smith began college in 1963, four black girls were killed when the Sixteenth Street Baptist Church in Birmingham was bombed as white separatists reacted violently to forced integration in schools.

When Carlos arrived in Austin, Texas from Harlem, with wife Kim and his daughter, he had asked about race relations. He was told by the college that they were "okay". "When we hit the airport I realised my mistake. A black man couldn't get a beer in a bar in Austin, the state capital," he said.

So he left. He returned to New York where he met Martin Luther King Jr, Rev Andrew Young and Harry Edwards, a former basketball star and discus thrower who taught sociology at San Jose State.

Leading up to the Games in the summer of 1968, the talk of protest by black athletes was such that a survey of black contenders in the US Olympic team, carried out by the magazine Track and Field News, showed that one third (nine out of 27) would at least consider a boycott. The US Olympic Committee (USOC), sniffing the air of rebellion, sent around a letter to all members of the team stating that anyone who didn't perform in honour of the US would be sent home from Mexico.

In February '68, Brundage's IOC, ignoring apartheid, made plans to re-admit South Africa to the Olympic Games. African and Caribbean nations, Cuba and the Soviet bloc were outraged. It was conceivable at that time that not one black athlete would take part in Mexico. The IOC backed down, though, and by April South Africa were again cast into the sporting wilderness.

In March, Carlos spoke with King in an effort to gel support for athletes who might boycott the Games in any case. On April 4th, King was assassinated in Memphis by James Earl Ray.

The days preceding the Games were marked by political unrest. When the Mexican government cleared away the street pedlars from Cathedral Square, one of the central areas of the city, students added their voice to the chorus of resentment over the government's bully-boy tactics. When Brundage sent a note to president Dias Ordaz, pointing out that if trouble spilled over to the Olympic arena the games would be cancelled, the reaction was to meet the protesters with extreme violence. On October 2nd, the students marched to the Plaza de las Tres Culturas. They were massacred. Officially, 257 died and 1,200 were injured. The numbers were probably higher. But the Olympics went ahead.

"I went back to my room at one stage during the Games, turned on the television and saw footage of the riots in Derry," says Carroll. "Dozens of students had been killed in demonstrations before the Games had even started, but there was absolutely no mention of that at all. It was all Northern Ireland. It was a very strange feeling being so far away from home and watching Derry on television in the middle of all this."

There was a mixed reaction from teammates to Smith and Carlos' actions. Bob Beamon, who had originally opposed any demonstration, soared 29 feet, 2 1/2 inches in the long jump, smashing the world record by almost 23 inches. He, along with bronze medallist Ralph Boston, wore the black socks of protest, but made no significant gestures.

In the 400 metres, a clean sweep by black Americans was inevitable. Lee Evans won in a world record 43.86 seconds, with Larry James in second and Ron Freeman in third. Evans had been convinced to run by Smith and Carlos, having initially decided to withdraw after the expulsion of his colleagues.

"They were pragmatic about the medal ceremony," says Carroll. "All the photographers who had missed the first picture of Smith and Carlos with their clenched fists arrived at the ceremony. There were thousands of them all expecting another gesture. But I know for a fact - because I was talking to the lads from Villanova - that the 4 x 400m relay was still to come and the athletes wanted a few more medals. There was no doubt they'd win it. So they did everything bar protest during the national anthem. They didn't insult the flag."

Black athletes won seven of the 12 American track and field golds, and set five world records and tied another. Black American women won three golds and set two world records. Wyomia Tyus became the first woman to win the Olympic 100 metres twice when she successfully defended her 1964 title. Despite the fact that the women had been excluded from the boycott deliberations, she dedicated her medal to Smith and Carlos.

Mexico's 7,350-foot altitude certainly assisted the record-breaking, but hardly explained why it subsequently took so long to break them. Smith's 19.83 seconds for the 200 metres lasted 11 years. Jim Hines's 9.95 for the 100 metres lasted 15. Evans's 43.86 for the 400 was not broken until 1988. Beamon's incredible leap survived until 1991 when Mike Powell surpassed the mark.

But Smith and Carlos did not survive the passage of time as healthily as the image of their gestures. Carlos was contacted last week in his job in Palm Springs, California, where he works as a school attendance officer.

"I don't want to do any interviews," he told The Irish Times. "Coz when I do bad no one calls, but when an anniversary comes along they all wanna talk to me and no one wants to give me any money. So I'm not doing anything. You understand that. You understand what I mean. I'm sorry man. Thank you for calling."

Carlos and Smith's gestures have lived with them and changed them. Both have since led low-key lives.

Smith had a peripheral role in the Cincinnati Bengals squad for three years before his American Football career spluttered out. He then taught sociology and coached athletics in Oberlin College, Ohio, but failed to secure tenure. His family endured some poverty and he applied for jobs in the Los Angeles sanitation and police departments before moving to Santa Monica in California where he still works as a track coach, withdrawn and almost reclusive.

Both athletes found it incredibly difficult to find employment after Mexico and suffered a year of death threats. Neither of their marriages lasted. Carlos's wife committed suicide in 1977. Carlos lived in LA and stumbled around. He took odd jobs, worked as a bouncer for $65 a week and left behind a string of other menial jobs. In 1986, he was arrested and found guilty of cocaine possession.

Both men changed the terms of the race debate by raising their arms. And they paid a price. The question now is whether they made a lasting difference to black America.