Thousands of people came to Washington for Saturday's march
Thousands of people have attended a rally in Washington to mark 50 years since Martin Luther King's famous "I have a dream" speech on civil rights.
Jobs, voting rights and gun violence topped the concerns of many of those who marched to the Lincoln Memorial.
Eric Holder, the first black US attorney general, said he and President Barack Obama would not be in office had it not been for the original marchers.
Mr Obama will mark the event on the actual anniversary next week.
Among those who addressed Saturday's rally was the mother of Trayvon Martin, a black teenager shot dead in Florida last year, whose killer was recently acquitted.
"He's not just my son, he's all of our son and we have to fight for our children," Sabrina Fulton said.
Earlier she told the BBC many young African Americans had been left afraid by the acquittal of neighbourhood watch volunteer George Zimmerman.
She called for a change to laws in many American states which allow the use of deadly force if a person feels seriously threatened.
Thousands of people marked the 50th anniversary of Martin Luther King's 'I have a dream' speech
Saturday's event comes a few days before the actual anniversary of the original march on 28 August 1963.
King, who was assassinated in 1968, led about 250,000 people to the Lincoln Memorial on the National Mall and delivered his famous speech from its steps.
"I have a dream that my four little children will one day live in a nation where they will not be judged by the colour of their skin but by the content of their character." he said, in one of the most celebrated pieces of American oratory.
Martin Luther King III, King's eldest son, told the marchers from the same steps on Saturday: "This is not the time for nostalgic commemoration nor is this the time for self-congratulatory celebration.
"The task is not done. The journey is not complete. We can and we must do more."
In his speech, Mr Holder said of the 1963 demonstrators: "They marched in spite of animosity, oppression and brutality because they believed in the greatness of what this nation could become and despaired of the founding promises not kept."
The spirit of 1963, he said, now demanded equality for gay people, Latinos, women, the disabled and others.
Organisers had hoped to gather some 100,000 people in Washington. The crowd was predominantly African American but included white Americans and others.
Mr Obama, the first black US president, is due to commemorate the event on Wednesday with a speech from the same spot where King spoke.
He will be joined by former Presidents Bill Clinton and Jimmy Carter, while churches and groups have been asked to ring bells at 15:00 (19:00 GMT) to mark the exact time King delivered his speech.