Witnesses to history recall coming together under shared banner at March on Washington

(CBS News) At the Lincoln Memorial, 50 years ago today, 250,000 Americans gathered as Martin Luther King Jr. said, "I have a dream."

On Wednesday, President Obama will mark the anniversary of the March on Washington with his own speech from the steps of the memorial.

Reporting from Washington, D.C., "CBS Evening News" anchor Scott Pelley shared the remembrances of three people who were in attendance during King's speech that day.

Special section: MLK's Dream: 50 Years Later

Marian Wright Edelman, the founder of the Children's Defense Fund, who was a young activist at the time, told Pelley, "You don't have many opportunities in life to come together with folk to sort of say 'Here's where we are as a people, and here's where we wanna be as a people and here's where we can be as a people.' "

Andrew Young, former mayor of Atlanta, and also a former U.S. ambassador to the United Nations, said he knew the event was something big "when the trains started unloading from the south and a trainload from Philadelphia, and then the movie stars flew in."

And Julian Bond, who was a young activist on that day in the crowd singing "We Shall Overcome" and later went on to become a Georgia state legislator, recalled through the book 'The Bystander' by Nick Bryant how frightened official Washington was of the march. He read, "'All elective surgery in Washington was canceled, freeing up 350 beds for riot-related emergencies. In the event of a riot, a policeman or national guardsman would be stationed on every street corner in downtown Washington. They deployed 200 scout cars, 86 motorcycles, 20 jeeps, several police helicopters, 23 cranes to move broken down or disabled busses, 350 inmates were evacuated from jail in the district to make space for disruptive protestors. And the administration stations, an official just to the right of the Lincoln Memorial with a cut-off switch and a record turntable if militant protestors overran the speaker platform, the sound feed to the loudspeakers would be cut off and replaced by a recording of Mahalia Jackson singing 'He's Got the Whole World in His Hands.'"

However, instead of a riot, Bond said, "You had absolute peace. I think two people were arrested that day."

Watch Pelley's report above and be sure to tune in to his full coverage of the 50th anniversary events on CBS News and CBSNews.com throughout the day.