Barack Obama said he's "as hopeful as ever" about the future of the U.S. as thousands of Americans converged on Washington's Lincoln Memorial for a free concert to celebrate his inauguration as the first black president.

"Only a handful of generations have been asked to confront challenges as serious as the ones we face right now," Obama said Sunday. "Despite the enormity of the task that lies ahead, I stand here today as hopeful as ever that the United States of America will endure, that it will prevail, that the dream of our founders will live on in our time."

People gathered hours in advance for the event at the same site chosen by civil rights activist Martin Luther King Jr. for his 1963 "I Have a Dream" speech. The concert featured songs by Bruce Springsteen, Stevie Wonder, James Taylor, Sheryl Crow, U2 and Mary J. Blige; Martin Luther King III spoke, along with actors including Denzel Washington and Tom Hanks.

Obama sang along as Garth Brooks performed "American Pie." He and his wife, Michelle, rocked along to Blige and jumped to their feet as Wonder sang and played the keyboard. Interspersed in the event were clips of past presidents, including the inaugural addresses by John F. Kennedy and Franklin Delano Roosevelt.

Obama and his wife followed incoming Vice President Joe Biden and his wife, Jill, down the steps of the memorial and waved to crowds that stretched down the National Mall to the Washington Monument before the concert. They took seats to the side of the stage with the Obama children, Sasha and Malia.

"Change has come to America," actor Jamie Foxx told the roaring crowd, quoting Obama and doing an impression of him that drew laughter from attendees and the president-elect himself.

Biden spoke about 40 minutes into the program about the value of work, saying it was about dignity and respect.

"I see a country built by men and women who believe in the dignity of work, who take pride in providing for their families," Biden told the crowd.

Obama, 47, for the second day chose to invoke the spirit of Abraham Lincoln, the president who led the U.S. through the Civil War and ended slavery. Obama arrived in Washington last night after a "whistlestop" train trip that began in Philadelphia; Lincoln arrived by railroad in 1861 for his own inauguration. Both were elected from their adopted home state of Illinois.

Sunday morning, Obama and Biden laid a wreath at the Tomb of the Unknowns at Arlington National Cemetery, just outside Washington. The cemetery dates back to the Civil War, and the tomb honors the remains of unidentified U.S. soldiers.