WASHINGTON -- President-elect Barack Obama said it could take several years for the economy to turn around, news obscured Sunday by an inaugural concert that saw crowds stretched along both sides of the reflecting pool in front of the Lincoln Memorial 

The "We Are One" concert marked the start of inaugural celebrations for Obama. 

The president-elect and his wife, Michelle -- rock stars of a different kind -- arrived to cheers as they walked down the steps of the memorial. Obama delivered remarks in which he said that he is inspired by the people of every station, who came to the inauguration to show that they love their country and care about changing it for the better.

Noting the monuments all around them, Obama said what gives him hope "is what I see when I look out across this mall. For in these monuments are chiseled those unlikely stories that affirm our unyielding faith -- a faith that anything is possible in America.

"You proved once more that people who love this country can change it. And as I prepare to assume the presidency, yours are the voices I will take with me every day I walk into that Oval Office -- the voices of men and women who have different stories but hold common hopes; who ask only for what was promised us as Americans -- that we might make of our lives what we will and see our children climb higher than we did," he said.

But he also said for the first time that an economic turnaround could take years. 

"I won't pretend that meeting any one of these challenges will be easy. It will take more than a month or a year, and it will likely take many. Along the way there will be setbacks and false starts and days that test our fundamental resolve as a nation," he said.

Despite the sobering assessment, the party on the Mall was lively as the audience extended more than a football field in length and reached beyond the World War II Memorial. For most of the folks in attendance the star-studded performance was only visible on massive Jumbotrons.

Performers including U2, Beyonce, Garth Brooks, John Mellencamp and Herbie Hancock were on the bill. Brooks said it was well past time that all the different musicians from multiple genres should appear. Organizers said virtually everyone asked to participate agreed to come to Washington for the show.  

Bruce Springsteen sang "The Rising" to open the concert with the help of the choir, taking a song best known as a call to action following the 2001 terror attacks and using it to usher in a new era in American politics.

The crowd, expected to reach a half-million, gathered in temperatures above the freezing mark. It was a welcome relief from the frigid weather that had gripped the nation's capital.

Earlier in the day on Sunday, D.C. Mayor Adrian Fenty said the size of the crowd at the concert would be the city's first dry run of security and also a good indicator of the audience to arrive on Tuesday for the inauguration.

Actor Denzel Washington, noting the Lincoln, Washington and Jefferson memorials, set the tone at the concert by proclaiming that "on this day, we are inspired by the man we have elected to be the 44th president of the United States."

"We come here knowing that we are all in this together," Washington said. "We are one!"

Another speaker was actor Tom Hanks, who as Forrest Gump famously gave a speech at the monument steps and jumped into the reflecting pool. This time, he appeared in a dark suit and read a somber tribute to Abraham Lincoln.

Jamie Foxx brought many in the crowd -- and the Obamas -- to their feet by repeatedly urging those from Chicago to make some noise: "Chi-town, stand up!" he demanded.

Foxx then launched into a quick impersonation of the president-elect.

The Lincoln Memorial was a historically significant location for the concert. Besides Lincoln being a role model to Obama -- with the president-elect retracing part of Lincoln's whistle-stop train tour to Washington and planning to take the oath of office on the 16th president's bible -- the memorial itself is steeped in civil rights history. 

Martin Luther King, Jr. delivered his "I Have a Dream" speech there in 1963, during the march on Washington. More than two decades earlier, the singer Marian Anderson -- at the invitation of then-Interior Secretary Harold Ickes, father of President Bill Clinton's deputy chief of staff -- came to the steps to sing "My Country 'Tis of Thee" after the Daughters of the American Revolution refused to let her sing in at Constitution Hall. After that, Eleanor Roosevelt quit the DAR. 

Vice President-elect Joe Biden spoke briefly near the top of the event, extolling the dignity of work. 

"Work is more than a paycheck. It's about dignity. It's about respect. It's about whether you can look your child in the eye and say, 'Honey, it's going to be all right,'" The Delaware Democrat told the audience. 

Biden said he has admired working men and women as he has traveled around the country and said "we owe them the chance to go to work each day knowing they have the thanks of a grateful nation."

FOX News' Wendell Goler and The Associated Press contributed to this report.