In the opening line of his "I Have a Dream" speech, delivered at the Lincoln Memorial on Wednesday, Aug. 28, 1963, the Rev. Dr. Martin Luther King Jr. predicted that the March on Washington for Jobs and Freedom would "go down in history as the greatest demonstration for freedom in the history of our nation."

Fifty years on, we know he was prophetic.

But at the time, it was a bold statement, for there had been many examples in our country's history when Americans had screwed their courage and protested for a noble cause. One could point to the actions of the Sons of Liberty that led to the signing of the Declaration of Independence. One might also point to the anti-slavery movement that culminated in the American Civil War and the liberation of the slaves with the ratification of the 13th Amendment. Indeed, there had been many other protests, picket lines and parades up until that point in our history, to be sure -- some of them, like the suffragist movement, with far-reaching consequences that could redefine the roles of president and first spouse in 2016, with the potential election of our first female president.

But because of what radio and television were able to transmit in late August 1963, the March on Washington was witnessed by far more Americans than any previous demonstration, and from the deep vaults of American history, now flung open with a few taps on a touchscreen, images and sounds from that day are easily sampled as part of the stream of signal events that define our nation's memory.

Read it at The Root.