In bitter cold flecked by an occasional flurry, as hundreds looked on, the President's House memorial, which marks the site where George Washington and John Adams conducted their presidencies and where Washington held at least nine enslaved Africans, opened to the public Wednesday in a 45-minute ceremony.

Mayor Nutter and key historians and activists stood before a granite wall incised with the names of the nine as the official ribbon was cut at 12:45 p.m. Immediately, a great throng of people pressed forward into the commemorative exhibition, just north of the Liberty Bell Center on Independence Mall.

It was here that Washington held Oney Judge, Hercules, Austin, Richmond, Moll, Paris, Giles, Joe, and Christopher Sheels more than two centuries ago. Yet to many in the audience, including community activists who pushed hard for a memorial to those held in bondage, these nine speak loudly now to the contradictions, indignities, denials, and avoidance that still riddle race relations in the United States.

In an eloquent speech, Nutter emphasized the importance of the site and exhibition, linking them to an emerging public willingness to discuss the real history of race in the United States.

"We gather here today at this historic place in Philadelphia not for presidents but rather on behalf of millions of silent voices - the enslaved Africans upon whose backs great wealth was accumulated, both here in the North and in the South," Nutter said. "This place, 'The President's House: Freedom and Slavery in the Making of a New Nation,' is a critical part of the national history, and now it becomes a living story for us to impart to our children . . . and to each other."

The President's House, he said, embodies "the contradiction" between slavery and freedom at the heart of the nation's birth, and the opening of the installation inaugurates "the dialogue" about that contradiction.

The site consists of an architectural echo of the house that stood at Sixth and Market Streets, with the stories of the Washington and Adams presidencies outlined in text exhibits and on painted-glass wall panels.

But here the familiar lineaments of the Founding Fathers are viewed in the context of a nation willing to sacrifice the freedom of Africans for the bounty that their labor could bestow on a white elite.

The stories of the nine enslaved are told in video vignettes placed around the exhibit, and at the rear, a few feet from the door of the Liberty Bell Center, stands a memorial to the nine, and by extension to all those held in bondage in America.

Dominating the site as a whole is a large glass enclosure - the architects, Kelly/Maiello Architects & Planners, call it a "glass vitrine" - protecting the fruits of a 2007 archaeological excavation. Within, about 10 feet below street level, visitors can see the remains of house foundations, revealing both the world of Washington and Adams (who held no slaves), and the world of indentured servants and Washington's black chattel.

The archaeology anchors the site in the real world, making it possible to see stone tracery of the kitchen, where Hercules, Washington's cook, prepared meals, and where the enslaved and indentured servants gathered. A few feet away is the foundation of a large bow window, designed by the first president.

"This is the power of place," said Randall Miller, a professor of history at St. Joseph's University involved in the project since its inception in 2002.

"This could be nowhere else."

Design and construction of the $10.5 million memorial were managed by the city. Following Wednesday's ceremony, responsibility was transferred to Independence National Historical Park.

Michael Coard, a founding member of the Avenging the Ancestors Coalition, a community group that began pushing for a memorial in 2002, said he was ecstatic about the opening - although he was careful to call the exhibit only a first step in recovering a lost black narrative.

"History is being made today," Coard told the audience. He noted that his group was "founded for the sole purpose of making sure that the truth, the whole truth, and nothing but the truth would be told about this house, this President's House site.

"And that truth pertains to slavery, to the enslavement of my ancestors, our ancestors, by President George Washington at America's first White House, which was right here at this very site where we now stand."

Development of the exhibition has been bedeviled by controversy since amateur historian Edward Lawler Jr. published a scholarly article drawing attention to the long-vanished Washington house in January 2002. At the time, Independence Park was about to build a new home for the Liberty Bell, which would have compelled Liberty Bell visitors to walk over the unmarked spot where the first president quartered slaves.

The deep irony aroused anger in the black community, leading ultimately to a rewriting of Liberty Bell exhibits and, eight years later, to the opening of the memorial site.

"I think one layer of historical amnesia is being swept away," said Gary Nash, emeritus professor of history at the University of California, Los Angeles, who raised an alarm about the house eight years ago at the time of the Lawler article and news accounts. "And I think the process of civic engagement [in the project] is a very important part. . . . It was messy. It was protracted. It was bloody sometimes, but it was in the end very democratic."

After the ceremony, people became riveted by video dramas depicting Judge, who escaped from the house and lived out her life, poor but free, in New Hampshire; of Hercules, who escaped a year after Judge and vanished; of the 18th-century Haitian rebellion; and of the threat of black revolution creeping into the new nation.

Other visitors explored the small, confining slave memorial at the rear of the site, or read stories of Adams and his policies toward France, which at the time had thousands of supporters shouting their approval on Market Street.

But many were drawn to the glass window onto the archaeological remains, the dust of our past.

"I never knew George Washington owned slaves in Philadelphia until all this," said a Germantown man who would only give his name as Abdul.

"I'm supposed to be at work," he explained. "But I wanted to come down here and see this history. It's just amazing. I remember my big grandma telling me there were slaves in Philadelphia years ago. No else said that. They didn't teach it."

Abdul wanted his 9-year-old son to know about the enslaved in "the first White House," so he brought him along too. His son was taking cell-phone pictures of the stony ruins inside the glass box.

What did he think of it? The boy looked up. "Uncomfortable," he said, and turned back to the ruins.