A day-long celebration of the legacy of Martin Luther King has culminated in an appeal from President Barack Obama.
He urged the tens of thousands who gathered today on the National Mall to become modern-day marchers for economic justice and racial harmony.
Obama spoke from the spot where, 50 years ago today, King pleaded with Americans to come together to stomp out racism and create a land of opportunity for all.
Former President Bill Clinton recalled the impact of King's words 50 years ago.
Clinton told the crowd at the Lincoln Memorial that the speech "moved millions -- including a 17-year-old boy watching alone in his home in Arkansas."
And former President Jimmy Carter said King's efforts had helped not just black Americans -- but that he "helped to free all people."
Obama joined members of King's family to ring a bell that hung in the 16th Street Baptist Church in Birmingham, Ala., before the church was bombed in 1963.
That was just weeks after King's famous speech. Church bells rang out nationwide, to answer a call from King to "let freedom ring."