This article is the ninth in a series featuring clips from the American Archive of Public Broadcasting, which is working to digitize television and radio pieces so that they may be preserved for years to come. For more about the project, see our introduction to the series, where you'll also find a handy list of all the series' pieces so far.

To think of the March on Washington on August 28, 1963, is to call to mind four famous words: "I have a dream." You don't just read those words; you hear them. You know the cadence and the timbre of Martin Luther King Jr.'s voice; you know the words.

But the March on Washington was a full day's worth of events. There were speakers and music, tributes and prayers. There was John Lewis of the Student Non-Violent Coordinating Committee, and the national anthem sung by Marian Anderson. For 15 hours—15 hours!—the event went on, and for 15 hours straight, a collective of radio stations known as the Educational Radio Network broadcast it live up and down the eastern seaboard.

And here is the best thing about that: As the broadcast played, a quarter-inch tape at WGBH in Boston rolled, recording for posterity the audio of that day. According to WGBH, "These tapes ... are the only complete audio coverage of the broadcast in existence."