By the winter of 2010, with transformations reshaping almost every corner of New York, the most anxiously awaited project of all remained frustratingly stalled.

[Distant sirens] The World Trade Center site remained a civic embarrassment, a morass of tangled steel and concrete rising no higher than street level.

In early March 2010, angry construction workers rallied at the site to protest the long-stymied development.

Not long after, with public frustration on the rise, Mayor Bloomberg stepped in again and, having already taken charge of fundraising for the memorial, now donated tens of millions dollars out of his own pocket and personally led the effort to raise the remaining money from his circle of the city's wealthiest citizens.

Chris McNickle: Even though he had very modest jurisdiction over the overall problem, he took it on himself to make sure that things happened there, that a memorial got built-- because without a memorial, nothing else would get built-- and that decisions would be made that would allow buildings to rise on that site again.

Narrator: What began to emerge now was a vast civic space unlike anything ever seen before in New York, one that looked back in time, as well as forward, where the shattering reality of what had happened there and been lost coexisted with the irrepressible vitality of the city in a new public crossroad at the very heart of the oldest part of the city.

♪ Though it had undergone countless revisions, the plan for Ground Zero that now began to take shape remained faithful to the essence of Daniel Libeskind's original vision.

♪ As the outer circle of structures began to arise-- emblems of the future-- so, too, did the lineaments of the two extraordinary monuments to memory at the heart of the site-- one above ground and one below; one a luminous memorial, and the other a twilit museum.

The design for the memorial had been the outcome of a completely democratic and open worldwide competition, the largest design competition in history.

The winning entry was the vision of a little-known architect named Michael Arad, who was working at the time for the New York Housing Authority, designing police stations.

In collaboration with a brilliant landscape architect named Peter Walker, Arad had envisioned an 8-acre open space ringed with trees and dominated by two immense openings in the ground, where the towers had stood, each to be lined with giant falls of water, that plunged into a basin 30 feet below, then disappeared into another great void.

♪ He called it "Reflecting Absence."

♪ Inscribed on bronze rails surrounding the two basins were the names of the 2,983 people killed in the attacks, including the hundreds of firefighters and police officers who had run into the towers and died trying to save others.

♪ The memorial itself would be the first component of Ground Zero to be completed, opening on September 11th, 2011, 10 years to the day after the attacks.

♪ Between the two great voids of the memorial, meanwhile, work continued on an underground museum that led deep beneath the site down into a twilit underworld where the massive steel columns of the original twin towers had once come to rest on the granite bedrock of Manhattan and where what remained of the towers would dwell.

♪ Most imposing of all was the massive six-story tall slurry wall rising from the floor of the site, erected a half-century earlier to hold back the underground waters of the Hudson.

Beth Hillman: This slurry wall is a part of the retaining wall essentially built all the way around the site.

After 9/11, the wall was at risk of collapsing.

If the wall had collapsed, Lower Manhattan would have been flooded, subway tunnels, PATH tunnels.

It would have been that much more of a disaster.

Narrator: All around the center of the site, meanwhile, galvanized by the energies the memorial had unleashed, work above ground continued.

Soon, along the eastern edge of the site, on one of the streets newly restored to the grid, two massive office buildings began to rise-- 72 and 80 stories tall.

North of the footprints, an even taller shape began climbing into the sky.

On August 30th, 2012, the last column on the highest floor of One World Trade Center was guided into place by high-steel ironworkers from the Kahnawake Mohawk Territory in Quebec, whose fathers and grandfathers had erected much of Manhattan's skyline over the previous century.

At 1,368 feet, the massive tower was far and away the tallest structure in New York.

When a slender shaft was hoisted into place, the building reached the ringing number it had aspired to from the start-- 1776-- making it the tallest building in the Western Hemisphere.

♪ Steve Plate: When you look at this project, it's not just rebuilding an area, it's rebuilding New York because when those towers fell, we had a mission.

I'm a Bronx boy.

My wife's a Queens girl, and we knew that we needed to help rebuild, and we spent over a decade doing that.

We showed the next generation how to respond.

♪ Narrator: Far below, another fantastic shape was emerging, the Port Authority's dreamlike, transportation complex-- designed by Santiago Calatrava-- called the Oculus-- whose astonishing wing-like exterior-- as if not to content to be among the lowest structures at Ground Zero--seemed on the verge of taking flight, ♪ The most life-affirming emblem of renewal at the site was also the most modest and unassuming.

The tranquil pedestrian plaza had been planted with 400 trees, all identical white oaks, except for one.

Before the memorial had even opened, workers had carefully replanted the Callery pear tree-- recovered, charred and broken, nine years earlier, and nurtured back to life by the Parks Department.

Called the "Survivor Tree," it had rapidly become a favorite among visitors and residents alike as a symbol of the city's resilience and vitality.