One Million Moms for Gun Control said the event was inspired by the Rev. Martin Luther King Jr.'s message of nonviolence.
A cabbie drove by beeping his car's horn and flashing a peace sign as some 400 marchers from the city's five boroughs and several other states, including Michigan, Minnesota and Florida, crossed the bridge.
Valerie Wright of Manhattan said she would have felt "negligent" if she didn't attend.
"Even though we just passed legislation here, it's more far reaching than just our state," she said.
Wright said it was important to be counted in the call for similar laws nationwide. "Sometimes showing up is the best thing you can do," she said.
Jennifer Edwards, from Ann Arbor, Mich., said she was not against guns, but wants a nationwide ban on military-style guns.
"If the man at Sandy Hook had a regular gun instead of an assault weapon, half of those children would be alive," she said of the Newtown, Conn., tragedy. "You can never stop people from doing crazy things, but if you can minimize it, if you can save one life, isn't it worth it?"
One Million Moms for Gun Control wants Congress to pass President Barack Obama's sweeping gun control proposals. Those include a ban on assault weapons and large magazines and closing loopholes that allow some gun sales without background checks. The group also is pushing for boundaries on how much ammunition can be purchased and limits on the scope of concealed weapons laws.
Last week, New York Gov. Andrew Cuomo signed the nation's toughest assault weapon and magazine restrictions.
The rally began with the rendition of "26 Names" by Tony-nominated actress Montego Glover. The song is a recitation of the Newtown victims' names set to music by Tony-winning composer Jason Robert Brown. Twenty first-graders and six school officials were killed in the shootings last month at Sandy Hook Elementary School.
It ended with comments from Shannon Watts, the group's founder, thanking those who marched through the frigid morning and imploring them to keep the pressure on to get national laws passed.
An Indianapolis resident, Watts said she was inspired by the Sandy Hook shootings to act. Using social media, word has spread so that in just a few weeks more than 75 chapters formed, including the one in Brooklyn that sponsored the event.
Watts said she envisions the group modeling itself after Mothers Against Drunk Driving, and hopes to lead a fight nationwide with rallies planned for next week in Washington and other cities.
"It's going to be a steady drip," she said. "We are not going to give up."
She acknowledged that others have fought the issue before, but said that the elementary school shooting was a turning point.
"This is a new generation of moms," she said.
Indeed, many in the crowd said they were galvanized by Newtown. Rachael Dubin, of Brooklyn, said she had never been involved in previous efforts to enact stricter gun laws, but the shootings were too close to home for the mother of a 2-year-old and a 5-year-old.
"It's the 5-year-old that really made what happened in Newtown so jarring," she said. "I think there absolutely needs to be national legislation, and I hope it's tougher than what was done in New York state."
The newcomers to the cause were joined by those who have been calling for stricter gun laws for years.
Jackie Rowe Adams, founder of Harlem Mothers SAVE (Stop Another Violent End), has buried two children because of gun violence.
"We can't bring our kids back, but we can certainly continue to do prevention, to do education and to do what we can to end the violence," she boomed at the rally.
Johnnymae Robinson lost her son in 1999, and marched in the Mother's Day rally in Washington in 2000 that was dubbed the "Million Mom March." She thought the strength of that effort would produce a bigger effect, she said, and hoped the momentum building now will produce some change.
Several members of the City Council, state Assembly and Senate joined the rally. Among them was Police Commissioner Ray Kelly, who has long called for stricter gun laws. He called the event a manifestation of the growing momentum for change. The commissioner said tighter laws on assault weapons are a start, but also added that handguns are used in most of the crimes within the city - most of them brought into New York illegally.
"We need a national policy to address that," he said.
Bennett Windheim of Manhattan brought his wife and son.
"This is a signal in support of what the president wants to do and sends a signal to legislators across the country that there's support for the president's initiatives."
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