"Dr. King said, There is nothing more powerful than the marching feet of a determined people," John Lewis, U.S. congressman and civil rights leader, told TIME. To commemorate the 50th anniversary of the March on Washington, TIME spoke to 17 people who helped make the event a success. Lewis, the sole surviving speaker from the day, sat alongside King on the steps of the Lincoln Memorial. Joan Baez and Peter Yarrow stirred the crowd through song. Harry Belafonte led a group of celebrities to attend in support. Photographer Bob Adelman was there to document history; King's speechwriter Clarence B. Jones had a hand in drafting it. Their memories of that day bring the march to life, conveying the optimism and energy of what was then the largest demonstration in American history.