ON THE evening of December 1, 1955, Rosa Parks boarded a bus in downtown Montgomery, Alabama. It was to be the most famous bus ride in American history, a bus ride that would spark civil rights protest across the American South and propel Parks to iconic status as the "mother of the civil rights movement".

At the time, Parks was a 42-year-old black seamstress returning home, weary from her day’s work and in some pain from an inflamed shoulder. As was customary for black passengers, she got on the bus at the front door and paid the driver, then got off the bus and boarded again through the back door. She then took her seat just behind the sign marking the "coloured" rear section of the bus. This was a movable sign, allowing the bus company maximum flexibility while upholding Alabama’s strict racial segregation laws.

As more white passengers boarded the bus, the white section at the front of the bus filled up, and one white man was unable to sit down. The bus driver decided to move the sign marking the coloured section back a row, and told Parks to give up her seat.

As there were no black seats left either, Parks would have had to stand. She refused to move. The driver called the police, who arrested Parks and took her to the city jail.

Racial incidents on buses were common across the South. From the end of the 19th century, the 11 states of the old Confederacy had imposed a system of white supremacy that included the disenfranchisement of black voters, discrimination in employment and education, and strict segregation in all areas of public life. It was a system sanctioned by the law and often upheld by violence.

But it was never a settled system. Black southerners challenged segregation repeatedly, never more so than on buses. Indeed, blacks in Montgomery had boycotted the buses for more than a year when segregation was first introduced in 1900. After the Second World War there were frequent skirmishes and arrests on the buses, but at the end of 1955 segregation seemed firmly entrenched across the South. However, the arrest of Parks precipitated a mass bus boycott by blacks in Montgomery that lasted for more than a year and culminated in the end of segregated transport and the first major breakthrough in the struggle against white supremacy.

When the bus driver challenged Rosa Parks, he picked the wrong person. She was one of the most educated black women in Montgomery. She was born Rosa Louise McCauley in 1913, to James McCauley, a carpenter, and Leona Edwards, a teacher. Her mother sent her to Montgomery Industrial School for Negro Girls, where she trained as a stenographer and a typist. When her mother became ill, Rosa had to cut short her education. But after marrying a local barber, Raymond Parks, Rosa resumed her schooling and at 20 she became of one the very few black high school graduates in the city.

At the time of her arrest Parks was also one of the most active and knowledgeable opponents of white supremacy in the state. Unable to get a job as a stenographer on account of her colour, Parks worked as a seamstress. But she put her typing skills to work in the service of the local branch of the National Association for the Advancement of Colored People, the main civil-rights organisation of its day. By the time of her arrest Parks was secretary of the branch, adviser to the branch’s youth council and had been involved in efforts to register black voting. She had also recently attended a two-week training course at the Highlander Folk School in Tennessee, a militantly liberal training school for civil rights campaigners, where she met the inspirational civil rights leader Ella Baker.

Black leaders in Montgomery had been pushing for a test case to challenge the treatment of black passengers on the buses. Even so, Parks’ refusal to stand up on the bus was not premeditated. "I did not get on the bus to get arrested," she said later. "I got on the bus to get home."

But it was conditioned by her increasing resentment at white supremacy and segregation. As she recalled later, "I was thinking that the only way to let them know I felt I was being mistreated was to do just what I did. I simply decided that I would not get up so a white person could sit. That I would refuse to do."

Nevertheless, Parks' arrest was opportune in every respect. She was mild-mannered, a committed Christian and well-known to many, and her arrest prompted an outcry and galvanised her community.

E.D. Nixon, president of the NAACP branch, called a meeting of black leaders. Jo Ann Robinson, the feisty leader of the town’s Black Women’s Political Council, distributed leaflets calling for a boycott. When the black leaders met, and to the consternation of some, community support for a boycott was unstoppable.