Washington (CNN) - President Barack Obama's address Wednesday from the steps of the Lincoln Memorial will commemorate the 50th anniversary of the Rev. Martin Luther King Jr.'s "I Have a Dream" speech, representing a symbolic moment in U.S. history.

On that day in 1963, when King and his fellow marchers attended what he labeled 'the greatest demonstration for freedom in the history of our nation," few in that crowd could have imagined that half a century later, the first African-American president of the United States would mark the occasion with a speech in the same location.