A decade after the Twin Towers were destroyed in the greatest attack against Americans on U.S. soil, there is visible progress in the efforts both to remember and rebuild. The completed memorial -- two expansive reflecting pools in the footprints of the fallen buildings -- will open to family members for the first time on the 10th anniversary of the attacks.
The memorial pools are nearly an acre each. Plaques line each pool, carved with the 2,983 names of those who died in the terror attacks Sept. 11, 2001. The memorial incorporated nearly 1,200 requests from victims' families to place the names near those of loved ones, co-workers and friends. It covers half of the 16-acre site, and contains 150 trees.
See the Memorial Here
Michael Arad, the architect of the World Trade Center memorial, said he wanted to make what was absent, visible.
"I think when you take in the scale of the space, and you see these close to 1,500 names that surround each pool, it's a moment of comprehension," he said. "It's not an easy moment, it shouldn't be, it's a sad moment. But it's a sad moment of understanding what happened that day. As you stand here I wanted people to be able to have that moment of quiet and thoughtful contemplation."
Work is continuing around the clock on projects at the site, including a transportation hub, multiple office towers and a museum dedicated to the 9/11 attacks. The museum is scheduled to open next year.
One World Trade Center is growing by a story a week, and will soon boast the title of the tallest skyscraper in the Western Hemisphere. Now 81 stories high, the new building will ultimately be 1,776 feet (105 stories), and will cost more than $3 billion.
Bill Baroni, deputy executive director of the Port Authority of New York & New Jersey, said they had a responsibility to make the building as safe as possible.
"We know that we have a moral responsibility to build this building stronger than has ever been built and taller than the Twin Towers before," he said.
David Childs, the architect of One World Trade Center, actually planned for the building to exceed New York's building code standards for safety.
"This building is as strong and secure as you could ever imagine," Childs told ABC News' Dan Harris. "There is a robustness to the design, in which columns are designed to take over for two or three other columns should they fall for some reason."
Childs designed the glass-encased building around a solid, concrete core. Elevators, sprinkler systems and wider staircases, including one dedicated specifically to first responders, are protected within the inner walls.
Rebuilding Visible at Ground Zero
The site has famously been a source of contention for everyone from politicians to developers, but it was many of the mourners who fought against rebuilding on what they called a sacred place.
"I think that's why it was so important that those people who felt immediately and understandably -- do nothing, leave this as a sacred site -- were wrong," Childs said. "It was an honor of the people that died there, they were working there, to rebuild and say, 'Pick yourself up.' It's in our DNA to want to rebuild after disasters."
Progress has been slow since the buildings fell amid a series of political and bureaucratic wrangling. Now, the work never stops. Construction has been nearly ongoing year round.
"It never stops," Baroni said. "We can't afford to stop."
Right now, there are 3,500 construction workers on all four corners of the site. By the time the project ends, Baroni said, 25,000 different construction workers will have worked on it.
Baroni said the schedule is set by a series of deadlines -- and the next one is for the museum -- set to open in 2012. Soon the office building will be finished, then the transportation hub, on which construction has yet to start.
"If you have to sum it all up in one word: progress," Baroni said. "Not a bad word, for a site that no one thought progress would ever happen."
ABC News' Dan Harris and Julia Bain contributed to this report.