They had waited for a speech which would change America

In just 35 words, the length of the presidential oath, a superpower changed for ever. One man brought, if briefly, a measure of unity to a divided world watching, live, in their billions, and a measure of joy to a country suddenly turning rather bleak.

In front of Barack Obama, a vast, multi-coloured carpet of people stretched back for a mile, as far as the Lincoln Memorial. Obama's had been a grassroots, insurgent road to the presidency, and the American grassroots wanted to witness its apotheosis. Across this immense nation, from the snows of Sarah Palin's Alaska to the baking deserts on the border with Mexico, the rest of America bore witness, too.

The ceremonial was low-key. The invited dignitaries walked through the Capitol building to take their places; one of the children was even chewing gum. But the modesty of it somehow underlined, not detracted from, the power of the moment.

Behind Mr Obama, on the other side of the Capitol building, waited the buses which were to transport some of his key aides to the White House straight after the handover of power, so urgent is the need to tackle the economic crisis.

Unseen, in the White House itself, a small army of domestic staff whisked the Bushes' last personal belongings off the shelves and the Obamas' onto them.

This new dawn for America had started, in fact, long before dawn. As early as two this morning, in the vicious Washington cold, gathered the advance guard of the crowd.

It was windy, and dark, and four degrees below zero. It was still two hours before they even opened the security gates onto the Mall, and 10 hours before Barack Obama became President. But these early arrivals, around 60 per cent of them black, had been waiting a lot longer than that for this day.

"I cannot tell you how important today is for me," said Richard Jarrett, from Allentown, Pennsylvania, who had gone without sleep to claim his place in the queue. "I already feel different as a black American. President-elect Obama said it changes how black children look at themselves. It changes how white children look at black children. I say Amen to that."

Near the dome of the Capitol, Johnson Copley, from Long Beach, California, had read aloud from a magazine the statement made by George H.White, the final representative of an earlier, false dawn of black emancipation in America. In the late 19th century, after the Civil War and the end of slavery, White was among a handful of blacks elected to Congress.

But as white supremacy regained its hold, they were expelled. On 29 January 1901, White, the last of them, on his last day in office, stood in the well of the House of Representatives and movingly foretold the day that has now, 108 years later, come to pass. "This, Mr Chairman," he said, "is perhaps the Negroes' temporary farewell to the American Congress, but let me say: Phoenix-like he will rise up some day and come again. These parting words are on behalf of an outraged, heart-broken, bruised and bleeding but God-fearing people The only apology I have for the earnestness with which I have spoken is that I am pleading for the life, the liberty, the future happiness, and manhood suffrage for one-eighth of the entire population of the United States."

As he read these words, Mr Copley had to keep stopping. He was crying, and I found it hard not to join in.

For the moment, this city of cynical, icy-veined operators has been briefly overwhelmed by genuine emotion.

But Washington being Washington, calculations are already being made of how this unprecedented gush of public goodwill — a 78 per cent approval rating — could give Mr Obama the greatest political clout of any post-war president.

He's certainly going to need it.