Calls for equality rang out from the steps of the Lincoln Memorial, each echoing Dr. Martin Luther King Jr.'s iconic address 50 years ago while reflecting a new generation's social and economic demands: more racial equality, an end to bias against gays and lesbians, better opportunities for the disabled, pathways to citizenship for undocumented immigrants and a renewed fight for workers' rights.
Wednesday's commemoration of the 50th anniversary of the March on Washington and King's "I Have a Dream" speech focused not only on how far the nation's fight for equality has come, but how far it has to go.
In the final speech of the day, President Obama said 50 years ago Dr. Martin Luther King “gave mighty voice to the quiet hopes of millions ... he offered a salvation path for oppressed and oppressors alike.”
The ordinary people watching the 1963 march were just as important as those whose names appear in history books, Obama said. And so were people who, when faced with bigotry, followed King's model of nonviolent progress.
"Many had gone to segregated schools and sat at segregated lunch counters, lived in towns where they couldn't vote and in cities where their votes didn't matter," Obama said. "There were couples in love who couldn't marry, soldiers who fought for freedoms abroad that they found denied to them at home.
"They had every reason to lash out in anger and resign themselves to a bitter fate. Yet they chose a different path."
Obama's message was largely an economic one, as those who fought for civil rights were also fighting for financial freedom. "The men and women who gathered 50 years ago were not there in search of some abstract ideal," Obama. "They were seeking jobs as well as justice."
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"Yes, there have been examples of success in black America that would have been unimaginable half a century ago," he said. "...City councils changed.... And eventually, the White House changed." But he referenced the fact that unemployment is twice as high among African Americans as it is for whites.
"The gap in wealth between races has not lessened; it's grown," Obama said. "...This remains our great unfinished business."
An estimated 100,000 people gathered on the Mall for the day's events, compared to estimates of more than 200,000 marchers 50 years ago.
One man in the crowd brought a picture of his father at the 1963 march. The sign was labeled "My father was here 50 years ago. I am following in his footsteps."
"It's important for me to be here," said Jesse N. Holmes, 56, of Northeast D.C. "It was very important for him to be here. I remember him leaving, dressed up in his suit, tried to get mother to go. He was a man who believed in racial equality. He was a community man, a family man, he wanted best for whole world. I want to continue those beliefs to speak up as he did. And I'm here to honor him."
The day also featured speeches from former presidents Bill Clinton and Jimmy Carter and from a list of civil-rights leaders and cultural figures.
At 3 p.m. Washington time, bells rang out across the nation's capital and the world, marking the moment King finished his speech in 1963.
Carter said he owed a personal debt to King, a fellow Southerner who backed Carter's bid for the presidency in 1976. Nodding to Presidents Obama and Clinton, Carter said, "It’s highly unlikely that any of us three to my right would have served at the White House, or would be on this platform, if not for Dr. Martin Luther King Jr. and his crusade for civil rights.”
And Clinton remembered watching the marchers converge on Washington 50 years ago.
"They opened minds, they melted hearts and they moved millions, including a 17-year-old boy watching alone in his home in Arkansas."
"Let freedom ring was Dr. King's closing call for a better and more just America," said Oprah Winfrey, one of the final speakers. "Today people from all walks of life will gather for bell ringing events all over our great country and the world, as we reaffirm our commitment to Dr. King's ideals."
"He challenged us to see how we all are more alike than we are different. So as the bells of freedom ring today, we are hoping it’s a time for all of us not only to reflect on the progress that we have made -- and we have made a lot -- but also to focus on ... what lies before us."
It was a message expressed throughout the day.
"We have not yet seen Dr. King's great vaults of opportunity open to everyone," said Dr. Eliza Byard, executive director of the Gay, Lesbian & Straight Education Network. "We have so far to go."
'He Changed Us Forever'
Rep. John Lewis passionately disagreed with anyone who would told him that little has changed since King's speech.
"For someone to grow up the way I grew up, in the cotton fields of Alabama to now serving in the U.S. Congress, it makes me want to tell them, 'Come and walk in my shoes'," he said.
"In 1963, we could not register to vote because the color of our skin." A so-called literacy test involved guessing the number of jellybeans in a jar, he said. "Medgar Evers had been killed in Mississippi. And that's why we told President Kennedy we intended to march on Washington."
Lewis praised King's peaceful message and its effect at the March on Washington.
"Not one incident of violence was reported that day," he said. "The spirit had engulfed the leadership of the movement and all its participants.... He changed us forever."
But, like other speakers Wednesday, Lewis conceded that there is still more to do.
"Those signs that said white and colored are gone, and you won't see them again, except in a museum or in a book or on a video," he said. But there are still invisible signs... that form a gulf between us.... The signs and scars of racism still remain deeply embedded in society."
Caroline Kennedy said her father, President John F. Kennedy, realized the country was facing a moral crisis in the 1960s, and that the work of the previous generation continues today.
"...We have suffered and sacrificed too much to let their dream become a memory," she told the crowd. "....Now it's our turn to live up to our parents' dream, to draw renewed strength from what happened here 50 years ago."
Kennedy said the crisis is far from over, citing the verdict in the George Zimmerman trial and what she called the Supreme Court's "evisceration" of the Voting Rights Act as examples.
'Proud and Inspired'
"America may have progressed with the election of a black president, and may soon progress with the election of a female president," said Mark Tillman, president of Alpha Phi Alpha fraternity, of which King was a member.
But, Tillman added, that progress cannot distract the country from the "burning realization that our journey is still challenging; [in] race and class, we still have a great distance to go."
Actor Forrest Whitaker told the crowd: "I remember the words of Dr. Martin Luther King Jr.: 'I have decided to stick with love. Hate is too great of a burden to bear'."
Martin Luther King III called on the crowd to continue his father's work, and not to fear the road ahead.
"I'm reminded that Dad challenged us, that's what he did, he challenged our nation to be a better nation," said King III. "....He often talked about [how] sometimes we must take some positions that are not safe... but our conscience tells us they are right."
Lance Matthiesen said he was "proud and inspired" after the speeches.
The Bethesda, Md. resident said he felt "fortunate, especially for my boys, for them to have opportunity to reflect on this moment and the benefits and struggles that the president just talked about."
"It's been a wonderful experience, to be in presence of this momentous occasion," said Irika Cheeks of Clinton, Md., who brought four kids with her.
"This is my first time seeing Obama -- it means a lot, and I'm excited to see him," said her son, 10-year-old lalacai.
Call for D.C. Statehood
The "Let Freedom Ring" commemoration event also featured speakers representing civil rights groups ranging from the union representing government employees to a group that organizes Jewish civil action.
The commemoration opened just after 11 a.m. with a solo trumpet performance of "When the Saints Go Marching In" by a student from D.C.'s Duke Ellington School of the Arts. Emcees Soledad O'Brien and Hill Harper welcomed guests and spoke on the historical significance of the day, thanking those who march 50 years ago.
Rain dampened the participants, and there were many reports of attendees having trouble getting through clogged security screening stations. Some reported that attendees passed out while waiting to get in.
But the speakers energized those who did get in, including civil rights icon Andrew Young, who infused his remarks with a rendition of "Woke Up This Morning With My Mind Stayed On Freedom."
D.C. Mayor Vincent Gray called on the crowd to join D.C.'s more than 600,000 residents in their pursuit for statehood -- a pursuit that Carter referenced, as well.
"We pay more than $3.5 billion in federal taxes but don't even get a final say in how we spend it locally," Gray said. "We must let freedom ring from the river of Anacostia...and we must let freedom ring to Capitol Hill itself."
Trayvon Martin's parents, Sybrina Fulton and Tracy Martin, also made an appearance on stage, joining Peter and Paul of Peter, Paul and Mary, in a song. The image of the 17-year-old who was fatally shot by George Zimmerman last year has been featured prominently in some of the week's events commemorating the anniversary of the "I Have a Dream Speech."
Martin was invoked several times through the day, as was voting rights.
Rev. Al Sharpton said, "We come today, not only to celebrate and commemorate, but as the children of Dr. King to face the children of Jim Crow. And just as our parents beat Jim Crow, we will beat James J. Crow Jr. Esq."
Many of Wednesday's speakers, including Maryland Governor Martin O'Malley, called on the crowd to take action and advance King's dream for equality.
O'Malley called for marriage equality, an increase in minimum wage and gun control.
"Thanks to Martin Luther King, America's best days are still ahead of us...," O'Malley said. "And in this great work, we are not afraid.
On Aug. 28, 1963, King stood at the steps of the Lincoln Memorial in Washington, D.C. and delivered the speech, with its ringing refrain, "I have a dream," to more than 250,000 civil rights activists and supporters gathered for the March on Washington for Jobs and Freedom.
The march became a critical turning point in the civil rights movement, and King's speech became known as one of the greatest in American history.
Wednesday, one group of early marchers began to walk to the National Mall at about 9 a.m., stopping at the Justice Department on their way to call for wider protection of voting rights.
Organizers say crowds of approximately 200,000 were expected.
The ceremony will close at 3 p.m. as Carter joins members of the King family and Georgia Rep. John Lewis -- who also spoke at the 1963 March on Washington -- in ringing a bell that hung in the 16th Street Baptist Church in Birmingham, Ala., before the church was bombed in 1963.
On Aug. 28, 1963, as King was wrapping up his speech at the Lincoln Memorial, he quoted from the patriotic song "My Country 'Tis of Thee," imploring his audience to "let freedom ring'' from the hilltops and mountains of every state in the nation, some of which he cited by name in his speech.
"When we allow freedom to ring -- when we let it ring from every city and every hamlet, from every state and every city, we will be able to speed up that day when all of God's children, black men and white men, Jews and Gentiles, Protestants and Catholics, will be able to join hands and sing in the words of the old Negro spiritual, 'Free at last, free at last, great God almighty, we are free at last,'' King said in closing.
More than 300 sites nationwide -- including each of the states King named in his famous speech -- will answer King's call by ringing bells at 3 p.m., in time with the ringing at the Lincoln Memorial.
Commemorations are planned as far away as Alaska, where participants plan to ring cow bells along with church bells in Juneau.
International commemorations will be held at London's Trafalgar Square, as well as in the nations of Japan, Switzerland, Nepal and Liberia.
"The response to our call to commemorate the March on Washington and my father's 'I Have a Dream' speech has been overwhelming,'' said King's daughter, the Rev. Bernice King, in a written statement.
Some of the sites that will host ceremonies are symbolic, such as the Brown v. Board of Education National Historic Site in Topeka, Kan., a monument to the landmark Supreme Court case that outlawed segregated schools in 1954.
Bells will also be rung at Lookout Mountain in Tennessee and Stone Mountain in Georgia, a site with a Confederate memorial that King referenced in his speech.
Washington National Cathedral will play a series of tunes and spirituals on its carillon from the church's central bell tower, including "Lift Every Voice and Sing,'' "Mine Eyes Have Seen the Glory,'' "Amazing Grace,'' "We Shall Overcome'' and "My Country 'Tis of Thee.''
King gave his last Sunday sermon at the National Cathedral, four days before he was assassinated on April 4, 1968.
Of the bell-ringing ceremony, the Very Rev. Gary Hall, the cathedral's dean, said, "It's a kind of proclamation of our aspirations for the expansion of freedom for all people. It's always important to remember that the civil rights movement started largely as a church movement.... It was essentially a group of black clergy with some white allies.''
On this historic day, share your dreams with NBC News by completing the statement, "I have a dream ______." Post your interpretation to Twitter, Facebook, Instagram and Vine using the "DreamDay hashtag.
If you're attending any events Wednesday commemorating the anniversary, use the hashtag #MLKDream50.