King was murdered in Memphis on April 4, 1968, while helping organize a strike by city sanitation workers. A protest march, with King in the lead, had been planned four days later.
Saturday's 4,000 marchers followed much the same route the original demonstration was to take. The march was among several held across the country Saturday to honor King's memory.
The Rev. Samuel "Billy" Kyles, chief organizer of a series of anniversary events called "Pilgrimage to Memphis," led the marchers under overcast skies with the Rev. Jesse Jackson; Memphis Mayor W.W. Herenton, the city's first elected black mayor; and Washington Mayor Marion Barry, a Memphis native.
The crowd, stretching for more than a half-dozen blocks, sang "We Shall Overcome," and other standards of the civil rights movement.
Many carried pictures of King or signs saying, "Remember the Man and the Message."
King's last march, on March 28 in Memphis, ended in violence when a group of rowdy young protesters began breaking store windows. Police moved in with clubs and tear gas.
The National Guard was called in the following day and the city was put under a curfew. King left town vowing to return to stage another march, this one peaceful.
But he never got the chance. King was felled by a single rifle slug on the balcony of The Lorraine Motel, now the National Civil Rights Museum, while preparing to go to dinner with Kyles, Jackson and other associates.
James Earl Ray, a prison escapee from Missouri, pleaded guilty to killing King and is serving a 99-year sentence at a Nashville prison.
But the debate over whether Ray was responsible for the civil right leader's death continues, as King's own family questions what happened three decades ago.
James Nelson, 34, carried a replica of the famous "I Am A Man" sign favored by strikers in 1968.
"This is history and I want to be part of it," Nelson said. "I want to make sure people my ageÂ…don't forget the dream. I don't want to let Dr. King down."
Jackson, addressing a rally at the end of the commemorative march, urged listeners to ask themselves what King would be doing now if he were alive.
"His focus was not merely black and white," Jackson said. "It was wrong and right."
King would be fighting still, he said, for better health care and economic equality and for "renewal rather than revenge."
In Atlanta, about 300 people gathered at the King's tomb. Two wreaths were laid at the foot of the tomb at the Martin Luther King Jr. Center for Nonviolent Social Change.
In New York, civil rights, labor and community activists led an estimated 4,000 on a march to Times Square.
"Today we call out for stength and shout out for courage hate will not live," said Jewelnel Davis, the Columbia University chaplain who began the march with a prayer.
By Woody Baird.
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