Several thousand gay-rights advocates turned the area around City Hall into a boisterous, rainbow-colored sea today joining others across the country in a simultaneous demonstration against California's new ban on gay marriage.

Protests took place in an estimated 300 cities, with demonstrators loudly criticizing California voters' passage of Proposition 8.

"This is the greatest thing I've ever seen in my life," said Philadelphia organizer Brandi Fitzgerald, looking out at chanting, sign-waving demonstrators on Dilworth Plaza.

At one point, the crowd pressed onto 15th Street, forcing police to redirect traffic by blocking one lane.

When that happened, a group of demonstrators fell in behind the flashing lights of a patrol car, and within seconds hundreds had stepped off the curb and into the street for an impromptu march.

"I didn't know there was going to be a march," one woman said to a friend.

"Me neither," the other answered. "Let's go."

And they did. At its longest, the march stretched three-quarters of the way around City Hall.

"People are ready to say, 'Enough is enough,' said Kevin Donlin, a human-resources employee at Thomas Jefferson University Hospital, who complained that U.S. marriage law discriminates against him and his partner.

It wasn't only gay men who protested today. Lesbians, bisexual, transgender and straight people gathered with clergy to raise public awareness about gay equality.

Almost daily protests have occurred in large California cities since election day. That's when voters passed Proposition 8 by 52.2 to 47.8 percent, overturning a May ruling by the state Supreme Court that legalized same-sex marriages.

Proposition 8 eliminated the right of gay couples to wed by amending the state constitution with a single sentence: "Only marriage between a man and a woman is valid or recognized in California."

Some funding for pro-Proposition-8 groups came from the Philadelphia area, with John and Josephine Templeton of Bryn Mawr contributing $1 million. Templeton, chairman of the John M. Templeton Foundation in West Conshohocken, is a major donor to conservative causes and the Republican Party.

Gay activists have cast their opposition to Proposition 8 as a civil-rights issue, saying that to ban marriage based on sexual orientation is the same as banning it based on color or religion.

Protesters gathered across the U.S. today under a banner of, "Stop the H8." In Boston and San Francisco, New York and Chicago, crowds vented frustrations, celebrated gay relationships and called for change.

"We are the American family, we live next door to you, we teach your children, we take care of your elderly," said Heather Baker, a special-education teacher who spoke at Boston's City Hall Plaza. "We need equal rights across the country."

Only Massachusetts and Connecticut allow gay marriage. All 30 states that have voted on the issue have enacted bans. Sometimes-violent protests followed the vote in California, and leaders of Join the Impact, which organized today's demonstrations, asked that ralliers be polite and respectful.

That's what occurred in Philadelphia. Organizers had hoped 1,000 would attend, and pledged to hold the rally rain or shine. As it turned out, drenching morning rain gave way to breezy sunshine, and the crowd size easily surpassed early goals.

Some people walked hand-and-hand with their same-sex lovers. Others pushed babies in strollers. People held signs reading, "Stop the H8," and, "You don't have to be gay to believe in civil rights."

Two representatives of the United Christian Church in Levittown held a banner proclaiming, "Never place a period where God has placed a comma," a sentiment attributed to comedian Gracie Allen.

"Not all Christians are opposed to homosexuality," said Sue Walding, who helped hold the banner. "We believe all people are equal in the sight of God."

Nearby, Kim Brown of East Germantown wore a sandwich board that bore language from the Constitution, with its guarantees of justice and liberty.

Brown said she's an American in every sense - a mother, a homeowner, a taxpayer, a Democratic Party worker. Yet as a gay woman, "I don't have equal rights."

Even after the rally ended, several hundred people gathered nearby to continue shouting slogans.

"It's not about race or religion anymore, it's not about gay or straight, it's about equality," said Fitzgerald, a 32-year-old photographer who is in a committed relationship. "Everybody deserves the same rights."

Contact staff writer Jeff Gammage at 610-313-8110 or jgammage@phillynews.com.

Inquirer wire services contributed to this story.