On August 28, 1963, Martin Luther King Jr. delivered one of the most important speeches in this nation's history. Incredibly, the most famous element of that speech, known as the "I Have A Dream Speech", was partly improvised and almost didn't happen.

King and his aides stayed up until around 4:00 a.m. the day of the March on Washington for Jobs and Freedom preparing his remarks. One of his aides, Wyatt Walker, reportedly advised King to cut any mention of the dream.

"Don't use the lines about 'I have a dream', he said. "It's trite, it's cliché. You've used it too many times already."

It's easy to see this as bad advice in hindsight, but King had indeed made frequent use of the dream refrain in appearances leading up to the march, including a speaking address just a week before in Chicago. King and his advisers agreed that the speech had to be different. It had to appeal not only to African Americans, but to a national audience hearing King for the first time.

If you watch the video of King's address before the Lincoln Memorial, you'll notice he's looking down at his notes during much of the first half of the speech. The words he speaks are powerful, but it would be the second half of the speech that would cement this as perhaps the greatest American speech of the 20th Century.

Halfway through his speech, at about the seventh paragraph, King took a pause. At that moment, gospel singer and personal friend Mahalia Jackson reportedly shouted, "Tell 'em about the dream!"

In that moment, everything changed.

King appeared more confident as he moved his notes slightly aside and surrendered himself to the moment he'd found himself in. He told the nation about his dream, drawing not only from previous speeches about it but from the genuine yearning in his heart to see it come true.

Instantly, an important speech was transformed into a legendary one that will echo down the corridors of human history.

Watch the speech below and join us in revisiting this incredible moment.