David Maraniss, an associate editor at The Post, is researching a book about Detroit in 1963.

Detroit, now so beleaguered, carries an important if largely unrecognized status on this 50th anniversary of America’s civil rights summer. It was here, on June 23, 1963, that Martin Luther King Jr. first publicly dreamed his dream. This was two months before his immortal speech rolled down from the Lincoln Memorial and into history books. King’s first enunciation of his powerful “I Have a Dream” riffs came not near a statue of the Great Emancipator on the Mall but inside Detroit’s Cobo Arena, at the end of what he hailed as “the largest and greatest demonstration of freedom ever held in the United States.”

Soon enough came something larger and greater — the March on Washington on Aug. 28 — and Detroit was largely forgotten. But the Walk to Freedom was first. At least 150,000 people walked down Woodward Avenue, Detroit’s main thoroughfare, on that hot summer afternoon, and although only 14,000 managed to press elbow-to-elbow into the arena to hear the speechifying at the end, a majestic wave of humanity washed across the surrounding streets and sidewalks and parking lots and lawns to listen over loudspeakers.

King spoke last, after a long-winded lineup of local politicians, ministers and labor leaders organized by the Rev. C.L. Franklin, chairman of the newly formed Detroit Council on Human Rights, pastor of New Bethel Baptist Church, and father of the soulful young rhythm and blues singer Aretha Franklin.

When, near the end, King thundered, “I have a dream,” audience members responded to the call and shouted, “Go ahead!” — and on he went. Some of his dream stanzas were nearly identical to those he would proclaim later in Washington; some more poetic, others less so. One seemed unique to that place. At one point, King spoke directly to a predominantly black Detroit audience that had endured decades of bank red-lining, exclusionary covenants and other Northern forms of de facto segregation. “I have a dream this afternoon that, one day right here in Detroit, Negroes will be able to buy a house or rent a house anywhere that their money will carry them and they will be able to get a job.”

Fifty years on, some parts of King’s dream are closer to reality than others, but none seems more deferred than his vision of Detroit, now a shell-shocked city on the brink of bankruptcy with long, lonesome stretches of abandoned buildings, foreclosed homes and a population devastated by joblessness. Detroit has become so synonymous with urban deterioration that it can seem too familiar, a cliche of hopelessness — a prevalent sensibility that robs people struggling to survive in Detroit, and to revive Detroit, of the respect they deserve.

Detroit has been decomposing, in a sense. All organic things decompose sooner or later, from human beings to cities, and then something new arises in their place. But they also leave important markers behind that shape the present and future. Detroit has left as many markers as any city in America. Cars, music, labor, civil rights — much of the mythical American dream was defined by this Detroit quartet. And all of them were in their fullness on that early summer day 50 years ago.

When King arrived for the Walk to Freedom, he was greeted at the airport by George Edwards, Detroit’s new police commissioner, a former and future judge who began his career as an organizer in Detroit’s automobile plants. Edwards had granted the permits for the march and instructed his officers to leave their clubs behind and put smiles on their faces. “You’ll see no dogs and fire hoses here,” he told King, referencing the violent police response that civil rights marchers had encountered two months earlier during demonstrations in Birmingham, Ala. King had been arrested in Birmingham, and thrown in jail there, and written his stirring call for unrelenting nonviolent resistance to segregation there (the “Letter from the Birmingham Jail”), and eventually was bailed out with money that came largely from Detroit — from Walter P. Reuther and his United Automobile Workers union.

Reuther’s union played a vital role that civil rights summer. Documents show that the auto workers contributed $114,981 to the movement in 1963, from the bail money in Birmingham to financial support for the marches in Detroit and Washington. Reuther had sat side by side with King and other civil rights leaders in the Oval Office the day before the Detroit march, discussing federal civil rights legislation with President Kennedy. He had sent out letters to UAW leaders in the Detroit region urging mobilization for the Walk to Freedom, saying the demonstration was “a matter requiring special effort” as one means of pressing for “unparalleled long-overdue action on the civil rights front.” And he was back in Detroit, again at King’s side, as they strode down Woodward Avenue at the front of the massive throng on the way to Cobo Arena.

Nothing will be the same when the Walk to Freedom is restaged Saturday in Detroit, on its 50th anniversary. King and Reuther are long gone, and so are most of the auto jobs. Detroit has been all but stripped of its home rule, a virtual ward of the state. The unions have been eviscerated. But everything seemed possible in Detroit in 1963. Jerome Cavanagh, the mayor, a Kennedy Democrat, was promoting the city as a model of urban planning. The Big Three auto companies were selling more cars than ever before. Reuther and his union leaders could envision a future of profit-sharing and paid sabbaticals for senior workers. Berry Gordy and his Motown records had America dancing in the streets to Martha and the Vandellas, Mary Wells, Marvin Gaye, Little Stevie Wonder, Smokey Robinson and the Miracles, the Temptations and the Four Tops.

Gordy was first and foremost a businessman, but he made all of the Detroit connections, from cars to music to civil rights. He had worked in the auto factories himself and had learned some of his music production methods from the assembly line. And he realized that his success went hand-in-hand with civil rights advancements. And King’s speech, his first dream, was recorded by Gordy and sold as an LP: “The Great March to Freedom, Rev. Martin Luther King Speaks.”

The recording was released by Motown on Aug. 27. The next day, the civil rights legions marched on Washington, and King spoke at the Lincoln Memorial, and Detroit was forgotten.