A new complex to replace the World Trade Center destroyed in the 9/11 attacks is taking shape. 

The 16-acre (6.5 hectare) site is owned by the Port Authority of New York and New Jersey, which is rebuilding the complex with developer Larry Silverstein. The total cost of the project is $14.8 billion.

Two of four office towers planned for the site have been “topped out,” which means the last beam has been set in place at the top. An above-ground memorial was finished in time for the 10th anniversary last year, and a transit hub is nearing completion.

But a payment dispute has delayed construction of an underground museum that had been expected to open in time for the 11th anniversary of the attacks. Plans for a performing arts center for the site also have been delayed, though a new board is reviewing designs, programming and fundraising goals.  Following is a list of the main parts of the complex.

THE MEMORIAL AND MUSEUM

The memorial features giant reflecting pools in the footprints of the twin towers, which are surrounded by bronze panels inscribed with the names of the victims. The above-ground plaza with 400 oak trees has been visited by more than four million people since it opened one day after the 10th anniversary.

But work ground to a halt last year on the underground museum, which will include biographies of the nearly 3,000 dead and the historical context of the attacks. The foundation for the memorial and the museum, which is run by Mayor Michael Bloomberg, claims the Port Authority owes it $140 million; the authority says it is owed $300 million.

The governors of New York and New Jersey have asked the National Park Service to help manage the National September 11th Memorial & Museum, and a bill has been submitted to Congress that would provide $20 million of funding annually.

The museum's displays include a granite staircase that withstood the attacks and allowed hundreds to escape, and the “Last Column,” which the New York Times likened to a steel shrine due to tributes inscribed by ironworkers and victims' families.

From the plaza, visitors will be able to look down through an atrium on two 70-foot-tall (21 meter) “tridents,” or steel branches, that supported the Twin Towers.

The Skyscrapers

* One World Trade Center: The $3.8 billion tower should open in early 2014, about five years behind schedule. German architect Daniel Libeskind, the site's master planner, envisioned a twisting “Freedom Tower” whose height of 1,776 feet (541 meters) matched the year of U.S. independence.

The final design by building architect David Childs of Skidmore, Owings & Merrill was more practical, though it will be the tallest building in the Western Hemisphere.

The 3 million-square-foot office tower is 55 percent leased.

Publisher Conde Nast has agreed to take 1.2 million square feet, the federal General Services Administration has leased over 270,000 square feet, and Vantone China has 190,000 square feet.

* Four World Trade Center: One of Silverstein's three skyscrapers was topped out at 72 stories in June and should open in the autumn of 2013. Designed by Japan's Maki and Associates, the 975-foot (297-meter) tower will be clad with a metallic mesh and is fully funded with insurance settlements and Liberty bonds, a subsidy Congress created to help revive New York City.

The 2.3 million-square-foot office tower will become the new headquarters of the Port Authority. The Port Authority and New York City have each leased 600,000 square feet.

* Three World Trade Center: Designed by Britain's Rogers Stirk Harbour + Partners, it will stand 1,080 feet high and its facade will feature diagonal supports when it opens, targeted for late 2014 or early 2015. With his insurance proceeds, Silverstein will build the tower up to the “podium” level, seven stories high, so that shops can open. To build offices over the stores he must first raise $300 million, pre-lease 400,000 square feet (37,160 square meters), and secure $1.3 billion of Liberty bonds and taxable debt. The city, state and Port Authority will each contribute $200 million.

* Two World Trade Center: The design by Britain's Foster + Partners has a glazed crystalline form and a diamond-shaped summit and will be built only to the street level initially, with completion of the tower depending on securing office tenants, according to Silverstein. When finished, the 1,278-foot-tall (390-meter) tower will have 3.1 million square feet of space.

* Mass transit hub: The elaborate design by Spanish architect Santiago Calatrava has been repeatedly simplified to prune its cost, but the final price tag is expected to be nearly $4 billion.

The hub's two steel-ribbed wings will spring out from the oculus, a soaring glass roof that will bring natural light to the 250,000 passengers expected to travel through the hub each day.

Scheduled to be finished in mid-2015, the hub should smooth the way for riders by interconnecting 11 subway lines and the Path commuter trains that link New York to New Jersey.

Performing Arts Centre

Plans for a 1,000-seat theater to be designed by U.S. architect Frank Gehry have been modified repeatedly, as other projects took precedence and various arts groups flirted with the center, only to back out. The Joyce Theater of New York City, which presents dance companies from all over the world, plans to occupy the new center. A new board is reviewing designs, programming and fundraising goals. Building the center partly depends on how long it takes for the new mass transit hub to open because the site is the temporary home for the PATH.

Off Site

Two related projects border the area known as "Ground Zero."

* Seven World Trade Center: The 52-story, $700 million skyscraper just north of Ground Zero was the first Silverstein building to go up, and was completed in 2006. It replaced a building at the same address destroyed in the attacks. The skyscraper is fully leased.

* Five World Trade Center: This will occupy the site of the former Deutsche Bank building, just south of Ground Zero. The old building, irreparably damaged in the attacks, has been demolished. In 2007, a fire at the site killed two firefighters. Plans for the new building remain unsettled.