By Kevin Connolly
BBC News, Chicago
Barack Obama was given a rock-star welcome by his excited supporters
Chicago offered us its own spectacular countdown to the end of the longest presidential campaign in history.
The setting sun sliding down the glass faces of the great downtown skyscrapers marked the ebbing of the final hours.
As darkness came, the makeshift open-air stage in the middle of Grant Park became a bowl of light - the campaign which began with the poetry of hope and triumphed through the power of the internet ended at last with the blazing magic of theatre.
Laser beams fanned out into the sky across the park from the stage, forming an arch of blindingly intense light - probably the first political celebration in history that would have been visible from the Moon.
Mr Obama, who all through the campaign has enjoyed the luck to match his undoubted brilliance, was even lucky with the Chicago weather.
The long lines of supporters began forming halfway around the park four hours before the gates were due to open. They waited in shirtsleeves, enjoying the freakishly warm November sunshine.
When the gates finally opened they charged in, whooping and screaming with excitement - and in that moment you realised how Mr Obama won the presidency. It was rock-festival behaviour from what pollsters would call the rock-festival generation.
Hurricane of sound
The Democratic campaign reached out through the internet to the young and recruited an army of smart, energetic and committed volunteers - their tickets to this final rally were sent out, fittingly, on the eve of the vote by e-mail.
They followed the triumphs and occasional disappointments of election night on a giant screen, greeting minor adjustments to the vote in key states with gales of applause and reacting to bigger news, like an outright victory, with a hurricane of sound that would have frightened the Beatles off stage.
No-one who heard it will ever forget the tidal wave of sound welling from the depths of the crowd that greeted the news that Mr Obama had won - it rippled back through the crowd that stretched far into the darkness of the night and seemed to hang and echo between the downtown skyscrapers.
One of the extraordinary achievements of the Obama campaign has been to revive the art of the public meeting - an achievement owed in equal measure to the soaring, pulpit-tinged cadences of the candidate's oratory and to his ability to recruit and organise a crowd over the internet.
This was one of the most powerful of all those many public meetings - the crowd danced along to the Stevie Wonder song Signed, Sealed, Delivered and cheered whenever they caught a glimpse of themselves on the giant screens carrying cable news coverage into the park.
They were even able to watch John McCain's graceful concession speech in Arizona - in fact it seemed to me at some points in that speech that it was going down rather better here in Chicago than it did with Mr McCain's own supporters.
Mr Obama owes his election in part, of course, to the way the American economy has suddenly shown signs of collapsing under the stewardship of one of the most unpopular presidents of modern times.
But he owes it too to his own promise to be a conciliator, a man who will pull together the diverse threads of American society into a more coherent, united whole.
His supporters in the crowd, many of them weeping as he spoke, listened to him reach out to disappointed Republicans, assuring them that even though he hadn't got their vote, he still needed their help.
Those supporters see in the result of the night far more than the choosing of America's 44th president - they believe that in showing itself ready to vote for a black leader, America has chosen to be a better country, more equal and less divided.
Agent of change?
The night was heavy with the weight of unspoken history. In 1961, when Mr Obama was born, segregation in restaurants and schools - even buses - was gradually being outlawed in parts of the South, though discrimination was still deeply embedded.
Now he has been sent to Washington to lead this vast and powerful nation, a decision which will transform America in the eyes of the world and perhaps in its own eyes too.
So Mr Obama will always be remembered as a symbol of change, but he wants to be remembered as an agent of change too - and that won't be easy.
America is fighting recession and wars on two fronts - and Mr Obama's supporters expect him to make this a better and fairer country in which to live. He carries a heavy burden of expectation as he takes office.
Not for the first time, he found words suffused with poetry to define the moment as a sea of his celebrating supporters cheered in the darkness of the Chicago night.
He told them anyone who doubted the power of American democracy had had their doubts answered in the night's result.
It was a final chance to revel in his ability to conjure a phrase to capture a moment - from tonight, though, Mr Obama is not simply about the power of language any more. From tonight, he speaks the language of power.