It started with about 10 or 20 people, when short of an official announcement it was still speculation.
They sang. Someone brought a flag. And it grew.
By the time President Obama finished his remarks at about 11:45 p.m. Sunday, officially telling the nation that Osama bin Laden was dead, it began a celebration that would last well into Monday.
Hundreds gathered in Lafayette Square, across from the White House, many of them responding to bulletins on social-networking sites like Facebook and Twitter. They chanted “USA” and they periodically sang the national anthem and “God Bless America.”
It mattered little that midnight had arrived. People bicycled into the park, they ran, some even emerged from taxicabs, eager to join the widening sea of patriotism across from 1600 Pennsylvania Avenue Northwest.
Nathaniel Thomas, 27, biked in from the Adams Morgan neighborhood.
“I’m glad this chapter is over,” he said.
Matt Krimm, 40, of Southwest Washington, said he had two friends in the military who died in Afghanistan. So upon hearing the news about bin Laden, he drove to the White House. As the owner of a D.C. cigar shop, Mr. Krimm was handing out a special-edition cigar, one of which he smoked himself.
“This is a vindication for what those guys sacrificed so we can be out here today,” he said between puffs.
By 1 a.m., the crowd had grown to hundreds more. And the rows of people once two and three deep in front of the White House gates had now suddenly swelled to 10 and 12 deep and beyond.
People waved or wore flags of every size.
Julie Olson, 33, of Annandale, Va., arrived with a female friend and wore a cardboard-cutout tiara and a red-white-and-blue checkered toga.
“I grabbed my picnic tablecloth, and she grabbed a box of Fourth of July stuff, and we put it on in the car,” she said.
By about 2:30 a.m., the crowd began to thin, but some revelers seemed determined to stay.
By morning, others had come to take their places.
The groups were smaller but still enthusiastic.
At about noon Monday, Alexandria, Va., resident Jill Valencia proudly displayed a large American flag in front of the White House and shouted, “It’s a good day to be an American” as passersby took photos with the petite blonde wearing a patriotic long-sleeve shirt.
“Every day I’m proud to be an American,” she shouted. “But today I want to bust a gut.”
Ms. Valencia and several of her female friends decided to stand with the flag to show support for military families.
“We’re not celebrating a death,” she said. “We’re celebrating justice.”
One group of tourists grinned as they posed with newspapers heralding the president’s big news.
At the Newseum along Pennsylvania Avenue, small crowds lingered at the display of front pages from across the country, almost all of them with bold headlines and photos declaring bin Laden’s death.
The museum’s website crashed early Monday as online viewers looking for coverage overwhelmed the server.
Northwest Washington resident Stacie Hatziyannis was on break from jury duty, so she stopped by the museum’s outdoor display to take photos of the front pages.
Ms. Hatziyannis said she was “very excited but fearful of reactions” to the Al Qaeda leader’s demise.
She said she felt as if justice had been served and hoped bin Laden’s death provided some comfort to families and friend who had lost loved ones.
“I think he was the figurehead for everything that Americans had felt since 9/11,” Ms. Hatziyannis said.