On August 28th, 1963, at the March on Washington for Jobs and Freedom, Martin Luther King stepped to the podium in front of the Lincoln Memorial. Around 10 minutes into his speech, King sounded as though he were wrapping up when Mahalia Jackson, the gospel singer and King's friend, shouted: "Tell them about the dream Martin". He ignored her at first. Then she shouted again. He put the text to the left of the lectern, grabbed the podium and, after a pause more pregnant than most, started to riff.
King's adviser Clarence Jones turned to the person next to him and said: "Those people don't know it, but they're about to go to church."
It's 50 years since Martin Luther King gave the speech that stands as one of the nation's favourite addresses delivered by one of its most beloved figures. But "I have a dream" wasn't in the text of the speech and its mainstream popularity only grew after King was assassinated.
To listen and read in full, 50 years ago today.
And some powerful images and readings by contemporary figures on BBC Radio 4, see links at the bottom of the BBC page for interviews and discussion.