During the Jim Crow era, laws restricted black Americans from patronizing gas stations, restaurants and hotels.
So Harlem-based letter carrier Victor Green published the "Negro Motorist Green Book: An International Travel Guide" in 1936, when travel was not only inconvenient but embarrassing and potentially deadly.
"The Green Book," as it came to be called, was a game changer, with its listings of black-friendly establishments.
"It was like the African-American AAA Travel Guide," said writer Calvin Ramsey, who wrote a play and a children's book about the publication.
"To most people, Washington, D.C., is technically a Southern city," Ramsey said. "But for people in the South, going to the march was 'going north.' People going by car or bus relied on the Green Book."
The spring 1956 edition of the Green Book listed D.C. hotels, restaurants and "tourist homes."
Though the Rev. Martin Luther King Jr. spent the days before the march writing his "I Have a Dream" speech at the upscale Willard Hotel, black-friendly hotels were not common and could not accommodate the swell of visitors. Black- and white-run tourist homes operated like bed-and-breakfasts and provided safe, affordable lodging.
At tourist homes, "everyone was treated like a relative," Ramsey said.
"The Green Book" became an establishment. Green, its enterprising author and namesake, collaborated with Esso Standard Oil Co., which began carrying the booklet at its gas stations.
Ernest Green -- no relation -- was one of nine African-American students to first attend Little Rock Central High School in a desegregation of Southern schools. He used the book with his mother and aunt to travel from Little Rock, Ark., to Hampton, Va., for his sister's graduation.
"This was before the accommodation laws were passed," he said. "It was a survival tool."
To Ramsey, the mission of the book was tied directly to the mission of the 1963 march.
"Martin Luther King said the greatest thing you can do is to serve mankind," Ramsey said. "That's what Victor Green was doing."
Victor Green, a letter carrier for 44 years and a member of the National Association of Letter Carriers, sought to capitalize on his work experience for the black community.
"That's where the strength of the mailmen came in," Ramsey said. "They knew which homes were safe, which neighborhoods were agreeable. Letter carriers knew these communities better than anybody else throughout the entire year, not just for the March on Washington."
At the time, the Postal Service was one of the nation's largest employers of African-Americans, a fact that's still true, said Phil Rubio, an associate professor of history at North Carolina A&T State University and former letter carrier.
African-American postal workers "brought the labor movement into the civil rights movement and the civil rights movement into the workplace," Rubio said.
The Postal Service became a vehicle for many African-Americans into the middle class.
"It was a secure job," said Rubio. "Once you got in, you could have status. You were a government employee and you could save money, buy a home, send your kids to college."
Massachusetts state Rep. Benjamin Swan used the Postal Service for this purpose.
"When I got out of the Army in 1956, I didn't have a college education. I had the full intention to go back to school so I needed employment," Swan said. As a postal worker for 10 years, Swan supported his wife and two children, took classes at Howard University and chaired the Springfield, Mass., chapter of the NAACP.
In 1963, he chartered a train and three buses to take New England chapters to the March on Washington. Because the group did not stay overnight in the District of Columbia, Swan said he did not have to worry about Jim Crow laws as much.
"I did know of the book, but I didn't know it was called 'The Green Book,'" he said. "It was kind of understood there were certain places you could not stay."
"There will be a day sometime in the near future when this guide will not have to be published," Victor Green wrote in a 1949 edition of his work. "That is when we as a race will have equal opportunities and privileges in the United States. It will be a great day for us to suspend this publication for then we can go wherever we please."
Green died in 1960, three years before the march, but lived to see the power of Jim Crow laws begin to fade.
A year after the march, following the passage of the Civil Rights Act of 1964, Green's wish was fulfilled and "The Green Book" ceased publication.
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