Standing before the Lincoln Memorial, Rep. Joaquin Castro paid tribute Wednesday to Latino civil rights activists of decades past, and said they had drawn inspiration from Dr. Martin Luther King and other African Americans who fought for equality.

“We’re grateful for the struggles and the movements and the blood and the tears of all the civil rights pioneers,” Castro said at the National Mall, where thousands gathered to commemorate King's "I Have a Dream" speech in 1963. “I want you to know that this generation of Americans will not let that dream go, that we will carry on and make sure that this country lives up to the values and principles for which you fought so hard.”

The Texas Democrat, who is 38, was the only Latino lawmaker who spoke at the event.

Castro paid tribute to Latino rights leaders such as Willie Velasquez, the founder of the Southwest Voter Registration Education Project in San Antonio.

And he spoke of his parents.

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“My own parents in the 1960s were very involved in a movement inspired by Martin Luther King,” he said, “they were active in the Chicano movement, in the Latino civil rights movement.”

Speakers scheduled to address the crowd at the daylong anniversary commemoration included Presidents Barack Obama, Bill Clinton and Jimmy Carter, as well as Dolores Huerta, the co-founder of the United Farm Workers of America, which launched marches in California and engaged in a variety of civil disobedience activities to fight for better wages and working conditions for farm workers.

On Tuesday, in an interview with Texas Public Radio, Castro said it was important for younger Americans not to lose sight of the civil rights struggle decades ago.

"It’s really a good chance for the people of my generation to honor the work that was done by the civil rights pioneers of the 50s, 60s and 70s and also to think about how this generation of Americans must carry on that work," Castro said.

"Martin Luther King’s vision was, of course, essential to the African American community, but I think also extended beyond that," Castro said on the radio. "And we see that in his relationship with Cesar Chavez in the 1960s for example. And so when we talk about the 'dreamers' -- the dream act students -- we really are talking about an extension of that dream."

Marchers opened the drizzly day by walking the streets of Washington behind a replica of the transit bus that Rosa Parks once rode when she refused to give up her seat to a white man. Mid-afternoon, the same bell was to ring that once hung in the 16th Street Baptist Church in Birmingham, Ala., before the church was bombed in 1963.

Oprah Winfrey, Forest Whitaker and Jamie Foxx led the celebrity contingent.

Setting a festive tone for the day, civil rights veteran Andrew Young, a former U.N. ambassador and congressman, veteran, sang an anthem of the civil rights movement and urged the crowd to join in as he belted out: "I woke up this morning with my mind on freedom." He ended his remarks by urging the crowd to "fight on."

Robby Novak, the young comedian known as Kid President, followed him to the podium and exhorted the crowd to "keep dreaming, keep dreaming."

King's eldest son, Martin Luther King III, said blacks can rightfully celebrate his father's life and work, and the election of the first black president, but much more work remains. Even now, he said on NBC's "Today" show, drawing on his father's words, "many young people, it seems, are first judged by their color and then the content of their character."

The Associated Press contributed to this story.