As Barack Obama was sworn in as president of the United States, the National Mall in Washnigton, D.C., filled with hundreds of thusands of people who had come to see the official beginning of the first African-American president's second term in office -- which began on the same day that the nation celebrated Martin Luther King Day.

In a speech that's already being widely recognized as a high moment in the history of American political oratory, Obama laid out the challenges ahead, but used the refrain "We, the people," from the preamble to the Constitution to underscore that it's up to citizens to set the course of the nation.

This is a set of images depicting the faces of the Americans who came to their capital to see the inauguration.

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