"This is a realisation of a dream, ever since I was part of the civil rights movement. Obama is the person we need at this time, at this point in history," said 74-year-old John Saunders.
He had ignored two hip replacements and the biting cold of a freezing January day to attend the inauguration, enthusing "it's completely, absolutely worth it."
"For people of color this is a very special day. It is a watershed moment," said David Cole, who travelled from Leesburg in Virginia to the city, to join a tide of humanity flooding the city's National Mall.
Earlier as the Obama motorcade swept past on the way to the Capitol building, the crowd lining the route went wild.
"That was sweet! That's what I wanted. I wanted to (see) history, be a part of something huge, like this," said 19-year-old Lawton Parnell, who drove in from West Virginia.
The day had begun early for the crowds, as the first packed subway trains that began rolling towards the city from 4am.
Bleary-eyed, sleep-deprived and aching with cold, they rode in from the outer suburbs in Maryland and Virginia. Others, bundled up in several layers against the bone-numbing cold, streamed by foot down the city's wide avenues, a flood of humanity cheerfully, but single-mindedly, moving in one direction.
Fred Phillips, 62, an African-American psychologist 62 from Washington, came with his wife, and was overwhelmed with the emotion at taking part in the inauguration of the country's first black president.
"It's a milestone in race relations in the US. We're still not completely there but we can't go back. The hopes from my ancestors have been realised, the efforts have been rewarded and the prayers have been answered," he said.
Just before Obama took the oath of office, the strains of "Queen of Soul" Aretha Franklin singing "My Country Tis of Thee" reverberated across the steps of the sparkling white Capitol, and swelled across the crowds below.
"I'm happy, I'm cold, and I'm celebrating," said Hollywood star Denzel Washington, smiling for pictures alongside fans. He was one of the lucky few to win a close up view of the momentous occasion.
But despite the long wait and the worst economic problems facing the nation since the Great Depression of the 1930s, the crowds crackled with hope and optimism.
"I think Obama and his administration are going to electrify, bolster and solidify all the dreams and aspirations in America," said Patrick Kearns, 47, from Charleston, West Virginia.
"We need to be better neighbors in the world."
Under bright, sunny skies, even those watching from hundreds of meters away on one of the huge video screens set up for the event, were overjoyed just to be there.
"We woke up at three but it's worth it. I think it's history on its way. We just want to be there celebrating," said Mary Lloyd.
The tight security net proved confusing for many, and some waited hours in order to secure a place along the route of the parade which was later to accompany Obama and his family to the White House.
The streets resembled a burgeoning tent city with food stalls springing up in middle of the street and the smell of cooking meat on grills.
Military Hummer trucks blocked off civilian streets, as police and military reservists stood guard on every street corner manning concrete barriers.
Whole highways were empty and then turning a corner, the crowds began.
"We were in the holding pen for a good couple of hours. Mashed in like sardines," said Pamela Jones, 58, from White Plains, New York. "When we finally got through it really was, free at last, free at last."
On an office building at the juncture where Pennsylvania Avenue makes a turn toward the Capitol, two large banners were fixed where they would be seen by the current and future president.
"Welcome Mr President," said one. "Thank you Mr President," said the other.