In the shadow of the Washington Monument and steps away from the Vietnam War Memorial, the group demanded a halt to preparations for a possible war against Iraq.
On the stage, Jesse Jackson -- his voice amplified across several acres of Constitution Gardens -- shouted, "If we act out of fear and not hope, we get bitter and not better."
"Sometimes wars are necessary," Jackson said. "The Civil War to end racism was necessary. World War II to end fascism was necessary. Even the war to get (Iraqi leader) Saddam (Hussein) out of Kuwait was necessary. But now, we can do it a better way."
Similar demonstrations were scheduled Saturday in San Francisco, Chicago, London, Rome and other cities all over the world, organizers said.
"This is just the tip of the iceberg," said one of the organizers, 21-year-old Eli Pariser, in an interview. Pariser's organization, Move On, said it raised $1.6 million in nine days via the Internet for congressional candidates who voted against the Iraq war resolution.
Pariser said he was shocked and surprised at the number of people that had contacted him lately who wanted to participate and told him, "I've never cared about anything this much before in my life."
People arrived in Washington by the thousands in buses, vans and cars packed with students, parents, families, and senior citizens. There were Muslim women wearing headscarfs, Catholic priests carrying placards, and children with peace signs on their T-shirts. And the numbers were as large, if not larger, than the organizers predicted.
"They said we couldn't get 100,000 people!" shouted one of the organizers, Mara Verheyden-Hilliard, of Partnership for Civil Justice. "There are people as far as I can see. And we are growing!"
Organizers said the total surpassed 200,000, but police would not confirm any numbers.
The umbrella organization planning the protest was Act Now to Stop the War and End Racism (ANSWER). The demonstrators paraded along streets near White House, and participants represented a number of groups, including the Muslim American Society Freedom Foundation and the International Action Center.
In preparation for the march, a number of streets were blocked off and there was a significant police presence. Many officers were on horses or motorcycles; some were in full riot gear. But police stressed that their presence was only a precaution and that they did not expect any disruptions.
"They are a peaceful group," one officer said.
More than 30 people spoke against the war at the rally, including former U.S. Attorney General Ramsey Clark, the Rev. Al Sharpton of the National Action Network, and Ben Cohen of Ben & Jerry's Ice Cream.
Actress Susan Sarandon spoke as well. "I am here as a mother because I am afraid for my children," she shouted. "I'm afraid for our children. I'm afraid for the Iraqi children."
The group criticized Congress for not representing the people when it authorized Bush to use force if Iraq refuses to allow inspections and removal of weapons of mass destruction. They shouted in protest against the Bush administration's foreign policy, which many of them said was imperialist.
A man in a black suit, smoking a pipe, passed out leaflets that read, "Are you ready for a perma-war?" A young girl with a ponytail, probably 4 years old, held a placard saying: "Blessed are the peacemakers."
Two shirtless women, walking arm-in-arm, pasted stickers on their chests that read, "Stop the Iraq war."
One Vietnam War veteran, Damon Stuhltrager, drove from Pennsylvania with his wife and two kids. When someone walked by chanting, "Stop the war! End racism!" his 8-year-old boy, Jesse, asked, "Dad, what's racism?"
Jesse's mother said she wanted to bring the young boy to the rally so he could see that his mom and dad were for peace and not war.
"As far as understanding that children are going to die, he doesn't," she said. "And I don't think I want him to."
"The idea of war for an 8-year-old is a tough thing," she added.