President Obama led the ceremony Saturday marking the 50th anniversary of the Selma, Ala., "Bloody Sunday" march, hailing the men and women who fought for civil rights in the 1960s but also declaring that more work needs to be done for race relations in the United States.

“There are places, and moments in America, where this nation’s destiny has been decided," the president said. "Selma is such a place."

He spoke from the Edmund Pettus Bridge on which police, using clubs and tear gas, attacked civil rights demonstrators on March 7, 1965. The event is considered a watershed moment in the civil rights movement and helped lead to the passage of the Voting Rights Act.

“In one afternoon 50 years ago, so much of our turbulent history -- the stain of slavery and anguish of civil war; the yoke of segregation and tyranny of Jim Crow; the death of four little girls in Birmingham, and the dream of a Baptist preacher -- met on this bridge,” Obama said, turning to Rep. John Lewis, D-Ga., who was present at the march. “It is a rare honor in this life to follow one of your heroes. And John Lewis is one of my heroes.”

Obama was joined by a delegation that included the first family, former President George W. Bush and roughly 100 members of Congress, including Lewis, who was seriously injured in the march. Members of the group, which also included former first lady Laura Bush, joined hands on stage after the president's speech. 

Obama, his wife, Michelle, and their daughters, Malia and Sasha, then walked about a third of the way across the bridge, accompanied by Lewis, who has given fellow lawmakers countless tours of this scene. Bush, his wife and scores of others came with them before a larger crowd followed.

"We have come to Selma to be reminded that we have do the work that justice and equality calls us to do," Lewis said. 

Tens of thousands of others also attended the event. Congressional Republican leaders were absent from the event, but House Speaker John Boehner of Ohio released a statement.

"Today, 50 years after the Selma to Montgomery marches began, the House honors the brave foot soldiers who risked their lives to secure the blessings of liberty for all Americans," Boehner said.

Selma still struggles to overcome its legacy.

The city's population has declined by about 40 percent to 20,000 in the last 50 years and Dallas County's unemployment rate is nearly double the state average. Public schools in Selma are nearly all black; most whites go to private schools. Blacks lead the annual "Bloody Sunday" commemoration; whites lead an annual re-enactment of the 1865 "Battle of Selma" to attract Civil War re-enactors.

For Obama, the trip to Selma marks the continued celebration by the first black U.S. president of three of the most important civil rights milestones in America's tortured racial history.

“We gather here to honor the courage of ordinary Americans willing to endure billy clubs and the chastening rod; tear gas and the trampling hoof; men and women who despite the gush of blood and splintered bone would stay true to their North Star and keep marching toward justice,” Obama said Saturday.

In 2013, Obama spoke at the 50th anniversary celebration of Martin Luther King's "I Have a Dream" speech on the steps of the Lincoln Memorial. Last year, he addressed the 50th anniversary of the signing of the 1964 Civil Rights Act by President Lyndon B. Johnson.

Obama also looked forward, arguing that too much racism still persists in the United States and that the Voting Rights Act remains under siege.

“We have to recognize that one day’s commemoration, no matter how special, is not enough,” Obama said. “If Selma taught us anything, it’s that our work is never done."

He added: "Our march is not yet finished."

He said the Justice Department's report on the Ferguson, Mo. police department shows that not enough has changed in the country with respect to race relations.

“But I rejected the notion that nothing’s changed,” Obama said. “What happened in Ferguson may not be unique, but it’s no longer endemic, or sanctioned by law and custom. And before the Civil Rights Movement, it most surely was.”

Obama said last week that the family was coming to pay tribute "as Americans to those who changed the course of history" at the bridge.

"Not just the legends and the giants of the Civil Rights Movement like Dr. King and John Lewis, but the countless American heroes whose names aren't in the history books that aren't etched on marble somewhere — ordinary men and women from all corners of this nation, all walks of life, black and white, rich and poor, students, scholars, maids, ministers — all who marched and who sang and organized to change this country for the better," Obama said at a Black History Month observance at the White House.

Obama also addressed the issue of voting rights in his State of the Union address.

His administration has challenged southern states that have imposed new voting requirements, including showing picture identification before being allowed to vote and curtailing opportunities to vote early. Critics of those laws say they have disenfranchised mostly minority voters and set back the gains won by civil rights marchers, including those who crossed the Edmund Pettus Bridge.

A divided U.S. Supreme Court voted 5-4 in June 2013 to remove from federal law the most effective tool for fighting discrimination against voters. Ruling in a case from Shelby County, Alabama, the high court eliminated the Justice Department's ability under the Voting Rights Act to identify and stop potentially discriminatory voting laws before they take effect.

The Associated Press contributed to this report.