We are looking forward to displaying this monumental piece of American history

Steve Hamp President, Henry Ford Museum

Steve Hamp, president of the Henry Ford Museum in Dearborn, Michigan, described the 1948-model bus as "the most important artefact in the history of the civil rights movement" - although it is not certain whether this was the actual vehicle on which Rosa Parks was arrested.

Mr Hamp said the Ford museum in Dearborn planned to restore the bus and eventually put it on permanent display.

The Ford collection already includes the limousine in which President John Kennedy was travelling when he was assassinated in Dallas on 22 November 1963.

Segregation

Ms Parks, now 88 and in poor health, was employed as a seamstress at a department store in the Alabama capital of Montgomery.

Ms Parks' protest sparked off a year-long civil rights boycott

On her way home from work on 5 December 1955, she refused to give up her seat to a white man, when the bus became crowded, thus breaking the law.

Ms Parks was arrested and fined, sparking a year-long boycott of Montgomery's buses.

At the time, black passengers in Montgomery were required to pay their fare at the front door of the bus, then enter by the back door.

Besides having to give up their seats to white passengers, they were not allowed to sit across the aisle from them.

The incident led to a US Supreme Court decision that forced the city to desegregate its bus system and helped to fire the civil rights movement.

Controversial past

However, no bus number was written down on police records when Ms Parks was arrested, and there have been questions over the years as to whether it would be possible to identify the vehicle.

The Ford Museum said experts had determined that the bus was the one on which Rosa Parks made her protest.

But other historians have questioned whether it can be proved that the bus is the right one.

There were 45 bids for the bus in the auction, including one from the city of Denver, which had hoped to make it the centrepiece of the city's African-American research library.

"The whole civil rights struggle came from this. That's what's so unique about this item," Denver Mayor Wellington Webb said.