Nine years after the September 11 attacks, the long-delayed redevelopment of Ground Zero finally has gained momentum.

Redevelopment of Lower Manhattan’s World Trade Center site has been beset with problems: design changes, funding problems, and political squabbling. And, there wasn’t even much to see at the site for nearly a decade, save for the tops of cranes and a few rumbling trucks, as a tall fence wrapped the perimeter.

But nine years after the September 11 attacks, there finally are tangible signs of progress. A memorial and a tree-filled plaza will be completed next year, in time for the 10th anniversary. The museum will open in 2012. And the steel framing of One World Trade Center—now at 36 stories—is clearly visible above the fence.

While other aspects of the development, including four additional towers and a transit hub, won’t be finished for years, officials say the project finally has momentum.

“At the end of the day we’re going to have a showpiece here that we are enormously proud of,” said developer Larry Silverstein on Tuesday afternoon, at a press conference called to update the public on what’s happened in the past year. He was joined by Governor David Paterson, Mayor Michael Bloomberg, and representatives of the Port Authority of New York and New Jersey, the transportation agency that owns the land.

The officials spoke on the 10th floor of what is perhaps Ground Zero’s biggest success story so far: Seven World Trade, a 52-story Skidmore Owings & Merrill-designed office building that opened in 2006. And while all the speakers praised what construction they could see outside the floor’s tall windows, many also acknowledged the start-stop nature of the process thus far.

“While nothing happens in democracy as quickly as we would like,” Mayor Bloomberg said, “the truth of the matter is, democracy does get you to the right place, even if it’s sometimes painful and it sometimes takes some time.”

Here’s a look at the key elements of the site:

The Memorial

The memorial, designed by Michael Arad and Peter Walker, will feature two 176-by-176-foot pools, whose square shapes mimic the footprints of the Twin Towers. Water will cascade down the sides of the 30-foot-deep pools, whose walls will be inscribed with victims’ names. They will be the largest artificial waterfalls in America, officials say.

As of early September, 65 percent of the granite that lines the pools was installed, and all of the structure’s steel (8,150 tons) was in place. In addition, 75 percent of its concrete has been poured, says Joe Daniels, president of the National 9/11 Memorial & Museum, which will run the site. Pump rooms for the waterfalls are now being fitted, Daniels adds.

Work on the surrounding plaza also is moving along. In August, workers planted 16 of the 438 swamp white oaks planned for the site. They are being grown off-site to a height of about 30 feet and will rise an additional 50 or so feet. All of the trees will come from New York, Pennsylvania, and Virginia—three places prominently affected by the September 11 attacks.

The Museum

The seven-story, 120,000-square-foot museum, designed by Davis Brody Bond Aedas, will be located underground, with its lowest level sitting on bedrock 70 feet down. Visitors will enter through a pavilion and gradually descend into the raw, cavernous space via a gently sloping ramp. Ceiling heights in the cast-in-place concrete building will vary from 26 to 60 feet.

The museum will include remnants of the Twin Towers and September 11, such as a 60-by-60-foot original slurry wall, a fire truck and ambulance damaged during the attacks, and a 37-foot-tall steel column that survived the building collapse and became an impromptu memorial, covered in tributes. “This is a museum without a façade,” notes Steven Davis, FAIA, managing partner at New York-based Davis Brody Bond Aedas. “Traditionally, the icon houses the exhibit. Here, the icon is the exhibit.”

The museum also will include a facility run by the New York medical examiner’s office to continue processing unidentified human remains. Approximately 3,000 people died on September 11—2,600 of them in New York — and only 40 percent of families received remains, notes Alice Greenwald, director of the National 9/11 Memorial & Museum.

The Pavilion

The pavilion piece of the $610 million project will be a 45,000-square-foot stainless-steel-clad structure designed by Snøhetta, a Norwegian architecture firm. It will contain an atrium, 160-seat auditorium, and rest rooms.

Perhaps its most striking feature is pair of trident-shaped steel beams that were salvaged from the Twin Towers and are slated to be installed on-site this week. “It’s great to see a place that was a hole in the city becoming something actual and tangible,” says architect Craig Dykers, a Snøhetta co-founder.

While construction of the museum and pavilion, along with the memorial, have been notably delayed—a completion date of 2009 promised was initially promised—projects of this scope often take a long time to realize, says Daniels. He points out that Washington, D.C.’s World War Two and Vietnam memorials were finished decades after the events they commemorate ended. Plus, “nobody asks now if Central Park was on-time and on-budget,” he says. “They are just happy with what was built.”

One World Trade Center

Designed by SOM’s David Childs and located in the northwest corner of the site, One World Trade Center will rise 1,776 feet (including its antenna) when it’s finished in 2013. It will be slightly taller than the original One WTC, which measured 1,727 feet with its antenna. The building was referred to as the Freedom Tower until 2009, when the Port Authority renamed it for branding reasons, according to reports.

The design calls for a symmetrical, 3.4 million-square-foot tower with eight glass façade planes shaped like isosceles triangles and a cubic base clad in prismatic glass. As of September 7, the steel framing for 36 stories of the 104-story skyscraper was complete. In October, workers expect to add windows to these levels.

After languishing for years, the project received a financial boost this year. The Durst Organization announced a $100 million equity stake in the $3.2 billion project, and Conde Nast, the magazine publisher, said it likely will lease 1 million square feet.

Towers Two, Three, Four and Five

Emerging from the southeast corner of the site, meanwhile, is Tower Four, a 64-story, 2- million-square-foot high-rise by Fumihiko Maki. The framing for six levels is complete. Starting in November, the developer expects to finish a floor a week, with completion slated for 2013.

In August, ending a two-year impasse, Silverstein and the Port Authority finalized a deal whereby the agency would provide $1 billion in public funds for Tower Four. The deal also calls for $600 million in Port Authority and other public funds for Tower Three, a 1,137-foot skyscraper designed by Richard Rogers. But the deal has strings attached: Silverstein has to raise $300 million in equity and secure tenants for 400,000 square feet of the 2.1 million-square-foot building to qualify for the money.

Tower Two, a 78-story skyscraper by Norman Foster, meanwhile, likely will have its foundations poured in 2011, according to a Silverstein spokesman. Tower Five, by Kohn Pedersen Fox, will rise on a site now occupied by the soon-to-be-demolished Deutsche Bank; however, the Port Authority, which will build Tower Five, has not released any details.

Other Projects

Two other major projects planned for the WTC site will follow, like a Santiago Calatrava-designed station for New Jersey’s PATH train, with connections to nearby subway lines. Arches for the soaring glass-covered mezzanine that will be the centerpiece of the $3.2 billion project are now being installed, with completion expected in 2014.

But less is known about a Frank Gehry-designed arts center, whose proposed site, next to One World Trade, now serves as the temporary PATH station.

In the meantime, a 2,500-square-foot visitors center—designed by Ron Vega—in a former camera shop on nearby Vesey Street is open and bustling. The center, which offers models of the buildings planned for the WTC site, has drawn 1.1 million visitors since its August 2009 debut, Daniels says. “This is a pretty good reflection of future visitors to the site,” he says. “We’re happy with it.”