Obama at concert: The dream of our founders will live on * Story Highlights * President-elect Barack Obama speaks at inaugural concert * Obama and Vice President-elect Joe Biden visit Tomb of Unknowns * The concert is being streamed live for free on HBO.com WASHINGTON (CNN) -- Inauguration revelry began Sunday afternoon as thousands of people packed the National Mall in Washington for a free concert featuring big stars. President-elect Barack Obama addressed a roaring crowd after 90 minutes of high-energy acts such as U2, Mary J. Blige, Usher and Beyonce. "Welcome to this celebration of American renewal," he said. "In the course of our history, only a handful of generations have been asked to confront challenges as serious as the ones we face right now." "I stand here today as hopeful as ever that the United States of America will endure," Obama said. "That it will prevail; that the dream of our founders will live on in our time."