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Evoking Abraham Lincoln and the Rev. Martin Luther King Jr., President-elect Barack Obama launched a four-day inaugural celebration Saturday before thousands of chilled but cheering onlookers from Philadelphia to the nation's capital. He promised to bring the country "a new Declaration of Independence" -- free from small thinking, prejudice and bigotry.

Obama invoked a grand heritage of American giants as he appealed "not to our easy instincts but to our better angels," an echo of Lincoln's first inaugural address. He took note of the enormous challenges that lie ahead and promised to act with "fierce urgency," a phrase often used by the Rev. Martin Luther King Jr.

In Baltimore, his last stop before arriving in Washington shortly before 7 p.m., Obama remembered the troops at Maryland's Fort McHenry who defeated the British many generations before.

"It's time to take up the cause for which they gave so much," he told a crowd of about 40,000. "The trials we face are very different now, but severe in their own right."

Tracking Lincoln's historic path to Washington by riding a vintage railcar on his whistle-stop trip, Obama carried with him the hopes of a nation weary of war, frightened of economic chaos and searching for better days. Vice President-elect Joe Biden joined the journey en route, from his home in Delaware, and spoke for many when he said he was excited and ready for Tuesday.

Then, sobered by the challenges of governing, Biden added: "I think it's Wednesday we need to be ready."

Washington pulsed with anticipation of Obama's swearing in as the nation's first black president. The city was aflutter with preparations for four days of parties and pomp, shadowed at every turn by layer upon layer of security. For every banner or piece of bunting that was going up around the city, there was a concrete barrier or metal fence at the ready as well.

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Revelers eager to get a head start on the celebration already were flowing into the city.

Toni Mateo, 38, arrived on a packed train from Atlanta. It was a quiet ride at first, he said.

"I just screamed out `Obama,' and the whole crowd erupted," he said.

For all the travelers arriving in Washington, there were plenty headed the opposite direction -- fleeing the crowds, the security, and the winter cold.

For traveler Obama, there was a celebratory air as his train pulled out of the station at Philadelphia.

"Welcome aboard the 2009 inaugural train to D.C," the conductor intoned.

Obama's blue rail car was tacked onto the back of a 10-car Amtrak train filled with hundreds of guests, reporters and staff for the 137-mile ride to Washington. Along the way, Obama and his wife, Michelle, appeared on the back balcony periodically to wave to shivering crowds bundled up in blankets and parkas who had gathered by the dozens, the hundreds and more along the route.

One held a sign that read, "Happy Birthday Michelle," taking note of the future first lady's 45th birthday. Another, in Delaware, waved a placard that said, "We came from Massachusetts 2 C U."

The well-wishers hoped not just for a glimpse of the 44th president-in-waiting but for a cameo role in history.

Joan Schiff, 47, a small business owner who campaigned for Obama, turned out for his departure from Philadelphia.

"At some point, you look up and think, 'I am in a moment,"' she said.

Carolyn Tyson, 55, came from Medford, N.J. to catch Obama's stop in Wilmington. She arrived a good seven hours early, at 6:30 a.m., to see the new president. "It's unreal, it's surreal," she said of Obama's election. Tyson, who is black, said she never thought she'd see a president of color.

The heady, celebratory air was tempered, however, by the tumult of the times, and Obama was quick to acknowledge them.

"Only a handful of times in our history has a generation been confronted with challenges so vast," he said. "An economy that is faltering. Two wars, one that needs to be ended responsibly, one that needs to be waged wisely. A planet that is warming from our unsustainable dependence on oil."

"There will be false starts and setbacks, frustrations and disappointments," he said, "and we will be called to show patience even as we act with fierce urgency."

While talking about the future, Obama reflected on the past, echoing the words of the Declaration of Independence, Lincoln and President John F. Kennedy. He cited the founding fathers who risked everything with no assurance of success in Philadelphia in the summer of 1776:

"They were willing to put all they were and all they had on the line -- their lives, their fortunes and their sacred honor -- for a set of ideals that continue to light the world: That we are equal. That our rights to life, liberty, and the pursuit of happiness come not from our laws, but from our maker. And that a government of, by, and for the people can endure."

The president-elect's triumphant day started with a sober discussion of the country's future with 41 people he met during his long quest for the White House. Preparing to board the train, Obama said that "what's required is a new declaration of independence -- from ideology and small thinking, prejudice and bigotry."

Obama was to deliver a speech before as many as 100,000 at Baltimore's War Memorial Plaza. Pressing the inaugural theme of service and community, event planners also called for canned food drives in Wilmington and Baltimore to coincide with his stops.

Capacity crowds are expected at the inauguration celebration in Washington, and the 135-mile trip, various stops along the way, is aimed at allowing as many people as possible to participate in the celebrations.

In keeping with the theme of the 2009 Inauguration, "Renewing America's Promise," organizers said the events are being held in cities that are instrumental to that message.

The promise was realized in Philadelphia, defended in Baltimore and will be renewed in Washington, organizers said.

Before departing Philadelphia, Obama said the same perseverance and idealism that the country's founding fathers displayed will be required to overcome the problems facing America.

"What is required is a new declaration of independence, not just in our nation, but in our own lives -- from ideology and small thinking, prejudice and bigotry -- an appeal not to our easy instincts but to our better angels," he said to a cheering crowd at 30th Street train station.

Echoing themes of his presidential campaign, Obama emphasized the common values and dreams shared by Americans and declared that unity would not only "restore hope and opportunity in places that yearned for both, but maybe, just maybe, we might perfect our union in the process."

After his 11-minute speech, Obama and his family began their journey, accompanied by a group of "everyday Americans" who have met Obama or Biden at some point and told them a compelling story. There are 16 families coming from 15 states.

Somewhere between 1 million and 2 million people are expected to make their way to Washington for the swearing in ceremony and inaugural parade.

About 240,000 tickets have been issued for the festivities at the Capitol, with 28,000 seats.

FOX News' Major Garrett and The Associated Press contributed to this report.