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The pace of construction is so swift that any status report these days gets overtaken rapidly by the arrival of new beams and columns, rebar and concrete, pipes and conduit. About 2,000 construction workers are on the job, weekends included, officials said, and that number will just keep rising. Visiting the site brings to mind the tumultuous first impressions of arrival in New York City: People, vehicles and objects are headed toward you from every direction at startling velocity, and the only prudent thing to do is to keep moving.

Two years ago, it was difficult to imagine how the Port Authority of New York and New Jersey, which owns the site of the trade center and is building most of it, could ever finish the eight-acre memorial in time for the 10th anniversary of the attack, on Sept. 11, 2011. Today, it is difficult to imagine what would stop them (though, given the site’s tortured history, the possibility shouldn’t be completely dismissed).

The great square voids in the plaza marking where the twin towers stood are fully formed and almost entirely clad in charcoal-gray granite. Enormous pumps are standing by to send thousands of gallons of water cascading into the voids, creating what memorial officials say will be the largest human-engineered waterfalls in the United States. A metal fabricator in New Jersey is incising bronze panels with the names of all 2,982 victims of 9/11 and of the trade center bombing in 1993. And last weekend, 16 swamp white oaks began to take root on the plaza. Four hundred more will follow.

But in the public’s mind, it is still "ground zero" — as in, "When are they ever going to build something at ground zero?" Or as in, "ground zero mosque," the shorthand reference for the Islamic community center planned two blocks to the north. While much of the nation has been debating who should be allowed to build what on that site, a former Burlington Coat Factory store, little attention has been paid to the fact that things really are being built on the spot where something actually happened.

A recent editorial cartoon in The San Diego Union-Tribune depicted the Islamic center as a giant salt shaker on the "wound" of ground zero, drawn as an empty expanse of earth. Apart from the issue of the Islamic center, the cartoon stoked frustration among those working at the site. Just at the moment they have something to show for nine years’ effort — 300,000 square feet of underground space, the shell of New York’s third-largest train station and two skyscrapers on the rise — the image has been resurrected of a barren, silent pit.

There was some truth to that image as recently as 2008. The trade center site was a dust bowl in summer and mud pit in winter. The only visible sign of progress was the silvery 7 World Trade Center tower across Vesey Street.

So many conflicting demands were imposed on the site — it was to be a solemn memorial, a soaring commercial complex, a vital transportation hub, a vibrant retail destination and the keystone in Lower Manhattan’s revival — that none could advance. And the many competing players seemed unable to break the logjam for long. They addressed one another as "stakeholders" in public, but the stakes they wielded usually seemed destined for someone else’s back.

What seems, in retrospect, to have been a key turning point was the politically unpalatable prospect that the 10th anniversary would come and go without a permanent memorial. In 2008, prodded in part by Mayor Michael R. Bloomberg, who heads the memorial foundation, the Port Authority adopted new schedules, approaches and construction techniques. Dozens of firms, including many of the city’s leading developers, architects and engineers, are involved.

The progress since then has been visible, tangible and audible. You no longer have to be inside the sidewalk barriers to get that. Just stand on Church Street and take in the sight of two giant steel towers-to-be, framing a crazily angled forest of crane booms. Or you could try to cross Church Street against the frenzied, never-ending convoys of construction vehicles entering and exiting. Good luck.

Perhaps the most surprising phenomenon occurs at bedrock level, seven stories beneath the street, in the great chamber of what will someday be the National September 11 Memorial Museum. Here, the ceremonial "last column" from the twin towers already stands in a climate-controlled cocoon. At certain moments, the room echoes. Dull and distant noise is transformed into profound, inchoate reverberation.

As the ninth anniversary approaches, it has begun to sound like a memorial.

© 2010 The New York Times Company