Democratic rivals Hillary Clinton and Barack Obama have crossed presidential campaign paths for the first time in Selma, Alabama.
The top contenders for the Democratic nomination were speaking at a day-long series of events to mark a 1965 civil rights march in the southern US state.
Their attendance is being seen as an attempt to attract crucial black votes.
Polls show Mr Obama has been gaining ground among black voters over Mrs Clinton who is still the front-runner.
Forty-two years ago, the small town of Selma, Alabama, was the scene of a black civil rights march attacked by state troopers and police on what became known as Bloody Sunday.
'Shoulders of giants'
Mr Obama and Mrs Clinton each spoke before packed congregations in neighbouring churches, almost simultaneously.
"I stand on the shoulders of giants," Mr Obama said at the AME church used as a headquarters before the march by the civil rights leader the Rev Martin Luther King.
"I'm here because somebody marched for freedom. I'm here because you all sacrificed for me," he said.
Mrs Clinton, speaking at a packed Baptist church, recalled the courage of those who marched in 1965, saying America still faced injustice and that "we have a march to finish".
"Our future matters. And it is up to us to take it back. Put it into our hands and start marching toward a better tomorrow," she said.
Mrs Clinton was also joined by her husband and former President Bill Clinton.
The BBC's James Westhead in Washington says this is the first time she has used his immense popularity among African-Americans to give her a boost on the campaign trail.
The events show both candidates are trying to associate themselves with the civil rights legacy in an increasingly fierce tussle for the democratic nomination, our correspondent says.