It was often portrayed as a spontaneous, almost chance act of petty defiance - the sort of thing that anyone might do after a bad day at the office. And certainly Rosa Parks had no inkling of the effect it would have. Returning home by bus in Montgomery, Alabama, one winter evening in 1955, weary after a long shift's work as a seamstress at a local department store, she refused a request by the driver to give up her seat to a white passenger. Her punishment was to be remanded in custody and fined $14. But the deed would mark the true start of black America's struggle for racial equality, and make her name famous around the world.
Nor was it a random act of exasperation - but the defining moment of a career of campaigning for civil rights, which had begun more than two decades earlier and which would continue almost until her death.
She was born Rosa McCauley, into a South that mercifully no longer exists - a land of lynchings and burnings and the whiterobed night-riders of the Ku Klux Klan, an age when survival, rather than rights, was the most to which blacks could aspire. Her good fortune was to attend the Montgomery Industrial School for Girls, set up by a group of northern liberal women, who taught her self-respect: the awareness that blacks were entitled to the security, dignity and opportunity which whites took for granted.
In 1932, at just 19, she married Raymond Parks, an early pioneer of black civil rights; by 1943 she was secretary of the Montgomery branch of the National Association for the Advancement of Colored People (NAACP), the most prestigious and venerable US civil rights group, fighting (mostly in vain) to secure justice for blacks subjected to rape, flogging and illegal tied labour. In short, little had changed - including the system of segregated seating operated by Montgomery's City Lines bus company.
On 1 December 1955 she and three companions were sitting in the first "black" seats behind the white section at the front. But this quickly filled, and they were asked to vacate their row so that a single white could occupy it. After some grumbling, the other three agreed, but Parks did not. "I don't think I should have to move," she told the police who came to arrest her, with the quiet dignity that was her hallmark. "Why do you push us around so?" She was carted off, fingerprinted, jailed and fined. Normally that would have been the end of the matter; another "uppity nigger" cowed and taught her place. But matters acquired a rather different dynamic.
Rosa Parks would not be cowed. Instead she appealed, giving Alabama's brave band of civil rights lawyers a perfect platform from which to attempt a new breach in segregationism, after the Brown v Board of Education ruling of 1954 that outlawed segregated schools. Blacks meanwhile began to boycott the bus company en masse - even though 115 were arrested for the offence of "organised boycott" and many more, including Parks, lost their jobs. But protest continued.
Black congregations across the city made common cause, in the process creating the Montgomery Improvement Association, whose first President was a rising young minister called Martin Luther King. He would be fined $1,000 for his pains, and the Montgomery NAACP would be hamstrung by a string of local court orders. But the appeal was upheld. Segregated seating was declared illegal by the Supreme Court, and on 20 December 1956, federal marshals delivered the order to the Montgomery city authorities. After 382 days, the boycott was over. The US civil rights movement had won its first great victory.
But, for its protagonist, the consequences would be severe. Unemployed, constantly harassed and threatened, her husband driven to a nervous breakdown, Rosa Parks moved to Detroit in 1957. There, in the city-symbol of industrial America, with its large urban black population, she gradually rebuilt her life, working first as a seamstress again, and then in the office of the Democratic Congressman John Conyers.
Times meanwhile were changing across the country. Not yet in the South perhaps, but almost everywhere else, Parks became a national heroine. Streets and shopping malls would be named after her, Presidents would fete her at the White House. But she advocated the black cause with undiminished energy, chastising President George Bush in 1989 for his leadership: "Instead of having better ceremonies we need better programmes." So far-flung was her fame that in September 1994 Gerry Adams would visit Detroit to meet her, calculating that a few moments in the company of a truly peaceful civil rights activist would soften his own violent reputation.
By then, however, the US debate over race had moved on. Increasingly, affirmative action was deemed too favourable to minority races, while black America had become synonymous not with discrimination, but with crime - as Parks would find out in person. A fortnight before the Sinn Fein President visited, a young black crossed her doorstep in far less friendly and admiring mood, stealing $56 and injuring her so badly she had to go to hospital. Typically, Rosa Parks was unbowed. But the attack was proof even her time was past - that, for a younger generation, the heroic age of civil rights was merely a memory.