Denzel Washington will narrate PBS‘ The March, a documentary chronicling the dramatic stories behind the historic 1963 March on Washington, credited as being a watershed moment in the civil rights movement that helped usher in sweeping civil rights legislation.

Roger Mudd was among those who showed up at PBS Q&A for the documentary, premiering on August 27. Mudd was CBS’s anchor for the network’s anchor for the network’s dawn-to-dusk live coverage of the march. Mudd, a congressional correspondent, covering Capitol Hill at the time, said this afternoon, “It was a hermetically sealed existence.”

“I never heard much about what was going on outside,” he said, of his knowledge of the civil rights movement at that time. “My first-hand look at the marvelous men and women who participated in that… was for me a revelation and I dare say for the men and women on Capitol Hill.”

The march is best known as the occasion in which Dr. Martin Luther King, Jr. delivered his “I Have a Dream” speech, which he delivered from the steps of the Lincoln Memorial.  Addressing TV critics at the press tour, King aide Clarence Jones credited CBS’ “gavel-to-gavel” coverage – the network blew out its lineup to cover the march – for giving millions of viewers, in all of the country’s major media markets, the chance to watch King deliver a speech in real time, for the first time. “I am convinced that, aside from the content of what he said,  the sheer impact — people were taken aback by the extraordinary power of who he was… When you have a significant amount of broadcast time, in all of the major markets, with his speech, and the background of those more than 250,000 [marchers] — it was a game changer.”

The march sent  “a signal to the nation, particularly to the center of power that… it was no longer a regional movement but a national movement,” added Mudd. After President Kennedy’s assassination, President Johnson “was able to use that assassination as a major lever to get the civil rights bill through”  only because “the march was as successful as it was,” he insisted.