Article published on the 2009-01-20 Latest update 2009-01-21 13:03 TU
The crowd stretched two miles back from the Capital Building, all the way to the Lincoln Memorial.
At just after noon local time, Chief Justice John Roberts swore in Obama, before the roaring crowd.
With heavy symbolism, Obama chose to take his presidential oath on the same bible that Abraham Lincoln - the president who ended slavery - did. Lincoln was also a senator from Illinois before he held the nation's highest office.
After each surviving former president, along with their spouses, were announced to the gathered crowd and seated, the military band played "hail to the chief" twice, a final rendition for President George W Bush followed shortly by a first for Obama after he gave his inaugural speech.
Already at six o'clock in the morning, thousands of people were present along the route that Obama and his family will take through downtown Washington, having walked or taken the subway.
The Washington subway’s first trains of the morning were already packed to capacity at 4:00am. As of ten o'clock local time, the subway system had reported that 500,000 had used the public transport.
The atmosphere stood in stark contrast with the last inaugural ceremony for George W Bush in 2005, an event the Washington Times called "relatively small."
Then, Bush faced many angry protestors who hurled eggs from behind tall metal barriers before being pushed back by riot police with pepper spray.
The US Capitol building, where Obama would take his oath, was lit up as the crowds started pouring in.
Early traffic jams around the city appeared as an expected two million people flowed into the city to witness the historic event first hand.
Inauguration goers had to navigate a maze of security barriers, set-up to assure the President’s safety, with metal detectors and thousands of police officers on hand. Bicycles were even banned from the area for the duration of the ceremonies.
Later, Obama and his Vice-President Joe Biden plan to lunch with members of Congress, Supreme Court Justices and Obama's cabinet.