A decade after 9/11, the vision of what will stand at Manhattan's Ground Zero is starting to become a reality. And while the Twin Towers will never truly be replaced, Tracy Smith shows us what future generations will have to look up to:
It was the last thing any of us expected.
Architect David Childs saw it all from his office window: "Everything was in flame and smoke coming out of the buildings. And a young man was standing there at the window, and he turned to me with tears coming down his face, and said, 'Will it fall over?'
"And I immediately said, 'No,' because in the history of steel construction buildings, none has ever fallen over from an event like this, a great fire."
Almost from the moment the towers fell, the World Trade Center site was caught up in an emotional tug-of-war. Some wanted the sacred ground left alone. Developers saw a chance to build something taller, safer ... better than what was there before.
When it was finished in the 1970s, the original World Trade Center was, to many, nothing more than a huge and expensive eyesore.
The complex displaced an entire neighborhood in lower Manhattan, and seemed out-of-scale. Among New Yorkers, the joke was that the gargantuan twin towers were actually the boxes that the Chrysler and Empire State Buildings came in.
"It was not a great place," said Childs. "In fact, no architects liked it. It's not a very great building. And the plaza was awful: Cold, blank, dreary, unfriendly, couldn't get there. All the streets had been ripped out. The photographs of the site a week after show this great emptiness there."
More than 5,000 designs for the rebuild were submitted, and in 2003 architect Daniel Libeskin's plan for a memorial and office complex got the nod.
Libeskin's centerpiece building - temporarily dubbed the Freedom Tower - would rise 1,776 feet, a nod to Independence Day, with an offset spire that echoed the Statue of Liberty.
Skidmore, Owings and Merrill (the architecture firm that built some of the tallest towers on Earth) was brought in. SOM's David Childs kept the height, but changed the tower's shape.
"I wanted to do a building like an obelisk," said Childs. "That would be a real marker, a sculptural piece that said, 'This is where this great tragedy occurred.'"
Childs likened it to the Washington Monument, which he said any fifth-grade student could draw after a class trip to the nation's capital. The same, he said, "will be true here."
"That was important to you? That a fifth-grade girl could go home and draw this building?" Smith asked.
"Yes, in the sense that it would be an iconic building which would be not so much about itself, but as the marker for that event and this city," he replied.
In 2006 the building commenced.
OxBlue Construction's cameras captured the building going up in time-lapse video. Construction hasn't been THAT quick, but the pace is dizzying.
SOM's Kenneth Lewis and T.J. Gottesdiener are managing the project.
"It moves at a floor a week, which in our world is incredibly fast," said Lewis.
"How do you manage that?" Smith asked.
"Fortunately, the contractor does that," replied Gottesdiener.
Chris Ward, who runs the Port Authority of New York and New Jersey, gave us a tour from the ground up - all the way to the 75th floor.
Smith said it was cool to be at eye level with the Empire State Building: "But, speaking of the Empire State Building, you've heard the gripe that that only took a little bit more than a year to build?"
"Yeah, I hear it all the time," Ward said. "You know, look at it. It was built in the '30s. OSHA regulations, safety, security wasn't really heard of. People died building that tower. But, most importantly, it was built right in the middle of midtown. This isn't like building an office building in a parking lot. This is building an office building - perhaps the largest and most secure office building - in the most complicated site in America."
It's complicated, all right: One World Trade Center has been called the number one terrorist target, so its 186-foot base has no windows, and is massive enough to shrug off a truck bomb.
Each 60-foot column weighs 70 tons.
The building itself will be close to the same height of the old towers, but the actual construction is nothing like the original.