Aerial photo of the World Trade Center site, as it appeared on September 23, 2001.

The World Trade Center site (ZIP code: 10048), also known as "Ground Zero" after the September 11 attacks, sits on 16 acres (65,000 m²) in Lower Manhattan in New York City.^[1] The World Trade Center complex stood on the site until it was destroyed in the attacks; Studio Daniel Libeskind, the Port Authority of New York and New Jersey, Silverstein Properties, and the Lower Manhattan Development Corporation oversee the reconstruction of the site. The site is bounded by Vesey Street to the north, the West Side Highway to the west, Liberty Street to the south, and Church Street to the east. The Port Authority owns the site's land (except for 7 World Trade Center). Developer Larry Silverstein holds the lease to retail and office space in four of the site's buildings.^[2]

While the Port Authority of New York and New Jersey is often identified as the owner of the WTC site, the ownership situation is actually somewhat complex and ambiguous.^[3] The Port Authority indeed owns a "significant" internal portion of the site of 16 acres (65,000 m²), but has acknowledged "ambiguities over ownership of miscellaneous strips of property at the World Trade Center site" going back to the 1960s. It is unclear who owns 2.5 acres (10,000 m²) of the site, being land where streets had been before the World Trade Center was built.

Before the World Trade Center[link]

The western portion of the World Trade Center site was originally under the Hudson River, with the shoreline in the vicinity of Greenwich Street. It was on this shoreline close to the intersection of Greenwich and the former Dey Street that Dutch explorer Adriaen Block's ship, the Tyger, burned to the waterline in November 1613, stranding Block and his crew and forcing them to overwinter on the island. They built the first European settlement, albeit a temporary one in what would be New York City. The remains of the ship were buried under landfill when the shoreline was extended starting in 1797, and were discovered during excavation work in 1916. The remains of a second ship from the eighteenth century were discovered in 2010 during excavation work at the site. The ship believed to be a Hudson River sloop was found just south of where the Twin Towers used to stand, about 20 feet below the surface.^[4]

The area that was cleared for construction of the original World Trade Center complex was previously occupied by various electronics stores in what was called Radio Row. These streets and stores were demolished in the 1960s to make way for the World Trade Center.

September 11 attacks[link]

On the morning of September 11, 2001, two hijacked planes bound for Los Angeles were intentionally crashed into the two towers of the World Trade Center. The towers collapsed within two hours of the collisions.^[5] Islamic Terrorists affiliated with Al-Qaeda organized and executed the attacks. Nearly 3,000 people died. After the attacks, hospital workers and police officers began referring to the World Trade Center site as "Ground Zero".^[6]

Debris and clean-up[link]

Satellite image of the World Trade center site after the attacks with the location of the Twin Towers and other buildings in the complex superimposed over the debris field

The World Trade Center site 17 days after the September 11, 2001 terrorist attacks. Buildings surrounding the site of the collapsed towers are fitted with mesh to prevent further damage and large construction vehicles are being used to clear debris.

The collapse of the towers spread dust across New York City and left hundreds of thousands of tons of debris at the site.^[7] To organize the cleanup and search for survivors and for human remains, the New York Fire Department divided the disaster site into four sectors, each headed by its own chief.^[8] Early estimates suggested that debris removal would take a year, but cleanup ended in May 2002, under budget and without a single serious injury.^[9][10] Three years later, in February 2005, the New York City Medical Examiner's office ended its process of identifying human remains at the site.^[11]

According to experts, when WTC 1 (the North Tower) collapsed, falling debris struck 7 World Trade Center and ignited fires on multiple floors. The uncontrolled fires ultimately led to the progressive collapse of the structure.^[12] Portions of the South Tower also damaged the nearby Deutsche Bank Building, which soon became filled with toxic dust. By 2002, Deutsche Bank determined that its building was unsalvageable. By January 2011, the Deutsche Bank Building was finally completely demolished.^[13]

Cleanup workers trucked most of the building materials and debris from Ground Zero to Fresh Kills Landfill in Staten Island. Some people, such as those affiliated with World Trade Center Families for Proper Burial, were worried that human remains might also have been (inadvertently) transported to the landfill.^[11]

In August 2008, New York City firefighters donated a cross made of steel from the World Trade Center to the Shanksville Volunteer Fire Company.^[14] The beam, mounted atop a platform shaped like the Pentagon, was erected outside the Shanksville firehouse near the crash site of United Airlines Flight 93.^[15]

In December 2001, a temporary viewing platform at Fulton Street, between Church Street and Broadway, opened to the public.^[16]

On March 11, 2002, 88 searchlights were installed and arranged to form two beams of light shooting straight up into the sky. This is called the Tribute in Light, and was originally lit every day at dusk until April 14, 2002. After that, the lights were lit on the two-year anniversary of the attack and have been lit on each subsequent September 11 since then.^[17]

Archaeology[link]

In July 2010 a team of archaeologists at the site discovered the remains of a 32-foot (9.8 m)-long boat over 200 years old; it was probably made in the 18th century and dumped there along with wooden beams and trash in about 1810 to make up the land.^[18] The boat had been weighted to make it sink as part of foundations for a new pier. Samples of its wood have been taken for dendrochronology.

Rebuilding[link]

World Trade Center site layout

Above: The World Trade Center site prior to the September 11 attacks.

Above: Preliminary site plans for the World Trade Center rebuild.

Soon after the September 11 attacks, Mayor Rudy Giuliani, Governor George Pataki, and President George W. Bush vowed to rebuild the World Trade Center site. On the day of the attacks, Giuliani proclaimed, "We will rebuild. We're going to come out of this stronger than before, politically stronger, economically stronger. The skyline will be made whole again."^[19] During a visit to the site on September 14, 2001, Bush spoke to a crowd of cleanup workers through a megaphone. An individual in the crowd shouted, "I can't hear you," to which Bush replied, "I can hear you. The rest of the world hears you. And the people who knocked these buildings down will hear all of us soon."^[20]

In a later address before Congress, the president declared, "As a symbol of America's resolve, my administration will work with Congress, and these two leaders, to show the world that we will rebuild New York City."^[21] The immediate response from World Trade Center leaseholder Larry Silverstein was that "it would be the tragedy of tragedies not to rebuild this part of New York. It would give the terrorists the victory they seek."^[22] However, ten years after the attacks, only one building, 7 World Trade Center, has been rebuilt. Two buildings are in the construction phase currently, One World Trade Center and 150 Greenwich Street (known as Four World Trade Center). The original twin towers took less than three years from start of construction to be finished, and 5 years from the beginning planning stages.

Lower Manhattan Development Corporation[link]

Governor Pataki established the Lower Manhattan Development Corporation (LMDC) in November 2001, as an official commission to oversee the rebuilding process.^[23] The LMDC coordinates federal assistance in the rebuilding process, and works with the Port Authority, Larry Silverstein, and Studio Daniel Libeskind, the master plan architect for the site's redesign. The corporation also handles communication with the local community, businesses, the city of New York, and relatives of victims of the September 11 attacks.^[24] A 16-member board of directors, half appointed by the governor and half by the mayor of New York, governs the LMDC.^[25]

The LMDC had questionable legal status regarding the restoration of the World Trade Center site, because the Port Authority owns most of the property and Larry Silverstein leased the World Trade Center's office space in July 2001. But the LMDC, in an April 2002 articulation of its principles for action, asserted its role in revitalizing lower Manhattan.^[26]

Early proposals for redesign[link]

In the months following the attacks, architects and urban planning experts held meetings and forums to discuss ideas for rebuilding the site.^[27] In January 2002, New York City art dealer Max Protetch solicited 50 concepts and renderings from artists and architects, which were put on exhibit in his Chelsea art gallery.^[28]

In April 2002, the LMDC sent out requests for proposals to redesign the World Trade Center site to 24 Manhattan architecture firms, but then soon withdrew them. The following month, the LMDC selected Beyer Blinder Belle as planner for the redesign of the World Trade Center site.^[29]

On July 16, 2002, Beyer Blinder Belle unveiled six concepts for redesigning the World Trade Center site.^[30] All six designs were voted "poor" by the roughly 5,000 New Yorkers that submitted feedback, so the LDMC announced a new, international, open-design study.^[31]

2002 World Trade Center site design competition[link]

In an August 2002 press release, the LMDC announced a design study for the World Trade Center site.^[32] The following month, the LMDC, along with New York New Visions – a coalition of 21 architecture, engineering, planning, landscape architecture and design organizations – announced seven semifinalists. The following seven architecture firms were then invited to compete to be the master plan architect for the World Trade Center:

• Foster and Partners (Norman Foster)
• Studio Daniel Libeskind (Daniel Libeskind)
• Meier Eisenman Gwathmey Holl (Peter Eisenman, Richard Meier, Charles Gwathmey and Steven Holl), sometimes known as "The Dream Team"^[33]
• Skidmore, Owings and Merrill
• THINK Team (Shigeru Ban, Frederic Schwartz, Ken Smith, Rafael Vinoly)
• United Architects

Peterson Littenberg, a small New York architecture firm, had been enlisted by the LMDC earlier that summer as a consultant, and was invited to participate as the seventh semifinalist.^[34]

The seven semifinalists presented their entries to the public on December 18, 2002 at the Winter Garden of the World Financial Center. In the following weeks, Skidmore, Owings & Merrill withdrew its entry from the competition.^[35]

Days before the announcement of the two finalists in February 2003, Larry Silverstein wrote to LMDC Chair John Whitehead to express his disapproval of all of the semifinalists' designs. As the Twin Towers' insurance money recipient, Silverstein claimed that he had the sole right to decide what would be built. He announced that he had already picked Skidmore, Owings & Merrill as his master planner for the site.^[36]

On February 1, 2003, the LMDC selected two finalists, the THINK Team and Studio Daniel Libeskind, and planned on picking a single winner by the end of the month.

Rafael Viñoly of the THINK Team and Studio Daniel Libeskind presented their designs to the LMDC, which selected the THINK design. Earlier the same day, however, Roland Betts, a member of the LMDC, had called a meeting and the corporation had agreed to vote for the THINK design before hearing the final presentations. Governor Pataki, who had originally commissioned the LMDC, intervened and overruled the LMDC's decision.^[37] On February 27, 2003, Studio Daniel Libeskind officially won the competition to be the master planner for the World Trade Center redesign.

Libeskind's original proposal, which is titled Memory Foundations, underwent extensive revisions during collaboration with Larry Silverstein, and Skidmore, Owings and Merrill, whom Silverstein hired. Though Libeskind designed the site, the individual buildings have been designed by different architects.

Detailed information about Libeskind's Memory Foundations site plan can be accessed at LMDC's website.

While not all of Liebeskind's ideas were incorporated into the final design, his design and the public support it garnered did solidify the principle that the original footprints of the Twin Towers should be turned into a memorial and not be used for commercial purposes. As a result, Liebeskind's lawyers at the New York firm of Wachtell Lipton embarked on the multi-year negotiation process to frame a master plan for the rebuilding. <http://www.wtc.com/news/Silversteins-Army> The first step in this process, completed in 2003, was the "swap" in which Silverstein gave up his rights to the footprints of the Twin Towers so that they could become a memorial, and in exchange received the right to build five new office towers around the memorial. <http://www.americanlawyer-digital.com/americanlawyer/tal200709/?pg=5> The "swap" and the ensuing negotiations, which lasted for many years, have been referred to as the most complex real estate transaction in human history because of the complexity of the issues involved, the many stakeholders, and the difficulty of reaching consensus. <Scott Raab, Construction of World Trade Center, Esquire, May 24, 2007>

Towers[link]

One World Trade Center (previously coined the "Freedom Tower" by Governor Pataki) is the centerpiece of Libeskind's design. The building will rise to 1,368 feet (417 m), the height of the original World Trade Center north tower, and its antenna will rise to the symbolic height of 1,776 feet (541 m). The antenna's height refers to 1776, the year in which the United States Declaration of Independence was signed.

The tower was a collaboration between Studio Daniel Libeskind and Skidmore, Owings and Merrill architect David Childs.^[38] Childs acted as the design architect and project manager for the tower, and Daniel Libeskind collaborated on the concept and schematic design.^[39] According to a NY1 article on March 8, 2011, a plan to build a restaurant on top of One World Trade Center (to duplicate the Windows on the World restaurant of old) was scrapped entirely because of potential risk of rising costs to build and maintain the establishment over the benefits of having one at all.^[40] Also, one of the main tenants of this tower to be confirmed is the Condé Nast Publications company, once it officially opens.^[41][42]

British architect Norman Foster designed Tower Two, also known as 200 Greenwich Street. The building's distinctive slanted, diamond-shaped roof echoes Libeskind's original sketches for the building.

Richard Rogers Partnership designed Tower Three, or 175 Greenwich Street, which stands across Greenwich Street from the Memorial's two reflecting pools.

Maki and Associates designed Tower Four, also known as 150 Greenwich Street.^[43][44]

Tower 5 was designed by Kohn Pedersen Fox and will stand where the Deutsche Bank Building once stood. On June 22, 2007, the Port Authority announced that JP Morgan Chase will lease the 42-story building for its investment banking headquarters.;^[45][46] however, JPMorgan's March 2008 acquisition of Bear Stearns had put the future of the 130 Liberty Street site in question, as the company is now planning to relocate its headquarters to 383 Madison Avenue. Construction began on September 9, 2011.

7 World Trade Center stands off of Port Authority property. David Childs of Skidmore, Owings and Merrill designed the tower, which opened in May 2006. The project company also announced that all of the towers will be completed even with the effects of the late 2000s recession at the worst case before 2020.

Memorial[link]

A memorial called "Reflecting Absence" honors the victims of the September 11 attacks and the 1993 World Trade Center bombing.^[47] The memorial, designed by Peter Walker and Israeli-American architect Michael Arad, consists of a field of trees interrupted by the footprints of the twin towers. Pools of water fill the footprints, underneath which sits a memorial space whose walls bear the names of the victims. The slurry wall, which holds back the Hudson River in the west and was an integral part of Libeskind's proposal, remains exposed.^[48]

Walker and Arad were selected from more than 5,000 entrants in the World Trade Center Site Memorial Competition in January 2004. Construction of the memorial was completed before September 11, 2011.^{[49][50][51][52][53][54][55][56][57]}

Museum[link]

On October 12, 2004, the LMDC announced that Gehry Partners LLP and Snøhetta, a Norwegian architectural firm, would design the site's performing arts and museum complexes, respectively.^{[58] [59]}

The Snøhetta-designed museum^[60] will now act as a memorial museum and visitors' center, after family members of 9/11 victims objected to the building's original occupant, the International Freedom Center.^[61]

Gehry's performing arts complex will now house only the Joyce Theater, because the Signature Theater Company dropped out due to space constraints and cost limitations.^[61]

Transportation Hub[link]

Entrance to the PATH at the World Trade Center

Santiago Calatrava designed the World Trade Center Transportation Hub (its main asset being the PATH station ) to replace the old World Trade Center station.^[62] The Transport Hub will connect the PATH station and 1 New York City Transit Authority subway train to the ferry terminal, the World Financial Center and One World Trade Center on the west and the 2 3 4 5 A C E J N R Z New York City Transit Authority subway trains through the Fulton Street Transit Center on the East. One will be able to walk most of the way across lower Manhattan. The Port Authority will cool the new station, as well as the September 11 Memorial and Museum, via a heat exchanger fed by four pipes carrying water from the Hudson River.^[63] The cost for the transportation hub is estimated at $3.44 billion.^[64][65][66]

Other buildings[link]

St. Nicholas Greek Orthodox Church[link]

Government officials have backed down from a July 2008 deal to relocate the St. Nicholas Greek Orthodox Church, the only church destroyed in the September 11 attacks.^[67][68]

A deal has been reached between church officials, Governor Andrew Cuomo, and the Port Authority to have the church rebuilt on the same site, but three times the original size on October 14, 2011, according to NY1.^[69]

Criticism of progress[link]

An episode of CBS's 60 Minutes in 2010 focused on the lack of progress at Ground Zero, particularly on the lack of completion dates for a majority of the buildings, the main tower, 1 World Trade Center (previously known as the Freedom Tower) having gone through three different designs, and the delays and monetary expense involved. Investor Larry Silverstein said that the Port Authority's estimated completion date for the entire site was 2037, and that billions of dollars had already been spent on the project, even though Ground Zero "is still a hole in the ground." During an interview for the episode, Larry Silverstein said "I am the most frustrated person in the world...I'm seventy-eight years of age; I want to see this thing done in my lifetime.".^[70] However, it was noted that in early 2011, all 5 office towers of the World Trade Center are under construction with significant progress being made. All of the towers will be opened between 2012–2016, with the National September 11 Memorial & Museum already completed on the tenth anniversary of the attacks, on September 11, 2011. Criticism of progress and calls for redesigns were mostly made in 2008 and 2009, when progress at the site was clearly not being made.

Construction[link]

As of September 2011^[update], progress on the construction of the redesigned site is as follows:^{[71][72][73][74][75][76]}

• 1 World Trade Center – Construction began in April 2006; two years later, tower-foundation steel columns, concrete, and rebar had been installed. In 2006, the Port Authority took over from Silverstein Properties as the project's developer. Tishman Construction Corporation is the construction manager.^[77] The estimated completion date is 2013.^[78]
• 2 World Trade Center – Groundbreaking in July 2008. Will be completed in 2015.^[79]
• 3 World Trade Center – Groundbreaking in March 2008. Will be completed in 2014. In April 2008, excavation and preparations for foundation work took place.^[80]
• 4 World Trade Center – Construction began in 2008. Will be completed in 2013.^{[81][82][83][84]}
• 5 World Trade Center – Construction began on September 9, 2011.^[85] The Port Authority acts as the building's developer.^[86]
• 7 World Trade Center – Opened on May 23, 2006 and achieved LEED gold status.^[87]
• National September 11 Memorial & Museum – Partially complete. The Memorial opened on September 11, 2011, coinciding with the 10th anniversary of the attacks.^[88][89] The museum will open in September 2012.
• Performing Arts Center – Construction will begin after 2014 since a temporary exit from the PATH station will occupy the site until then.^[90]

Construction gallery[link]

• 

  A light still on at Ground Zero remains, 2001.

• 

  From the south, a view of ongoing excavation in July 2002. The slurry wall circumscribing the site is visible, as is the damaged Verizon Building in the background.

• Groundzero2002 cc.jpg

  Aerial view of the site from the northwest, 2002.

• 

  The World Trade Center site after cleanup, 2003.

• 

  Visitor and observation plaza, 2005.

• 

  Construction as of March 2, 2010. The frame for Tower 4 can be seen rising on the left.

• 

  Overhead, April 2010

• 

  From the 30th floor of the W Hotel, July 28, 2010

• 

  One World Trade Center on June 1, 2011. Tower steel is prepared to grow up to the 68th floor.

• 

  One World Trade Center on January 28, 2012. Glass has been placed higher than 7 World Trade Center.

• 

  Four World Trade Center under construction on March 12, 2012.

See also[link]

New York City portal

Wikimedia Commons has media related to: World Trade Center site

• Collapse of the World Trade Center
• Health effects arising from the September 11 attacks
• Survivors' Staircase
• Verizon Building
• Construction of One World Trade Center

References[link]

External links[link]

• Official site - Silverstein Properties
• Tribute WTC 9/11 Visitor Center
• Reviving Ground Zero - interactive slideshow with audio by The New York Times
• Downtown Restoration Program - Port Authority of New York & New Jersey
• National September 11 Memorial & Museum at the World Trade Center
• Project Rebirth
• World Trade Center Rising
• RebuildGroundZero.org, a community project based on Ground Zero's rebuilding.
• The Freedom Tower (YouTube)

Coordinates: 40°42′42″N 74°00′44″W / 40.711641°N 74.012253°W / 40.711641; -74.012253

World Trade Center[1]
The original World Trade Center in March 2001. The reddish-brown building (back left) is the original 7 World Trade Center. The North Tower (left), with antenna spire, is 1 WTC. The South Tower (right) is 2 WTC. All 7 buildings are partially visible (see map below). Background shows the East River.
Record height
Tallest in the world from 1971 to 1973[I]
Preceded by	Empire State Building
Surpassed by	Willis Tower
General information
Location	New York City
Coordinates	40°42′42″N 74°00′45″W / 40.71167°N 74.0125°W / 40.71167; -74.0125Coordinates: 40°42′42″N 74°00′45″W / 40.71167°N 74.0125°W / 40.71167; -74.0125
Groundbreaking	August 25, 1966
Construction started	1 WTC: August 1968 2 WTC: January 1969 3 WTC: December 1979 4, 5, & 6 WTC: 1970 7 WTC: 1983
Completed	1 WTC: December 23, 1970 2 WTC: July 19, 1971 3 WTC: February 1981 4, 5, & 6 WTC: 1975 7 WTC: 1987
Opening	April 4, 1973
Destroyed	September 11, 2001
Height
Antenna spire	1 WTC: 1,727 ft (526.3 m)
Roof	1 WTC: 1,368 ft (417.0 m) 2 WTC: 1,362 ft (415.0 m) 3 WTC: 242 ft (74.0 m) 4 & 5 WTC: 118 ft (36.0 m) 6 WTC: 105 ft (32.0 m) 7 WTC: 610 ft (186.0 m)
Top floor	1 WTC: 1,347 ft (411.0 m) 2 WTC: 1,341 ft (409.0 m)
Technical details
Floor count	1 & 2 WTC: 110 floors 3 WTC: 22 floors 4 & 5 WTC: 9 floors 6 WTC: 8 floors 7 WTC: 47 floors
Floor area	1 & 2 WTC:[clarification needed] 4,300,000 sq ft (400,000 m2) 4, 5, & 6 WTC: 500,000 sq ft (50,000 m2) 7 WTC: 1,868,000 sq ft (170,000 m2)
Elevators	Both had 99 elevators
Design and construction
Owner	Port Authority of New York and New Jersey
Architect	Minoru Yamasaki Emery Roth & Sons
Engineer	Leslie E. Robertson Associates

The original World Trade Center was a complex with seven buildings featuring landmark twin towers in Lower Manhattan, New York City, United States. The complex opened on April 4, 1973, and was destroyed in 2001 in the September 11 attacks. The site is being rebuilt with five new skyscrapers and a memorial to the casualties of the attacks. As of November 2011^[update], only one skyscraper has been completed; the other four are expected to be completed before 2020. One World Trade Center will be the lead building for the new complex, reaching more than 100 stories at its completion.^[2] It became the tallest building in New York City on April 30, 2012, and is expected to be finished by 2013. A sixth tower is awaiting confirmation.

At the time of their completion, the original 1 World Trade Center (the North Tower) and 2 World Trade Center (the South Tower), known collectively as the Twin Towers, were the tallest buildings in the world. The other buildings included 3 WTC (the Marriott World Trade Center), 4 WTC, 5 WTC, 6 WTC (which housed United States Customs), and 7 WTC. All of these buildings were built between 1975 and 1985.

The complex was designed in the early 1960s by Minoru Yamasaki and Associates of Troy, Michigan, and Emery Roth and Sons of New York.^[3] The twin 110-story towers used a tube-frame structural design. To gain approval for the project, the Port Authority of New York and New Jersey agreed to take over the Hudson & Manhattan Railroad, which became the Port Authority Trans-Hudson (PATH). Groundbreaking for the World Trade Center took place on August 5, 1966. The North Tower was completed in December 1972 and the South Tower was finished in July 1973. The construction project involved excavating a large amount of material, which was later used as landfill to build Battery Park City on the west side of Lower Manhattan. The cost for the construction was $400 million ($2,300,000,000 in 2012 dollars).^[4] The complex was located in the heart of New York City's downtown financial district and contained 13.4 million square feet (1.24 million m²) of office space.^[5][6]

The Windows on the World restaurant was located on the 106th and 107th floors of 1 World Trade Center (the North Tower) while the Top of the World observation deck was located on the 107th floor of 2 World Trade Center (the South Tower). The second King Kong film was filmed in 1976 with some scenes mentioning and showing the World Trade Center.

The World Trade Center experienced a fire on February 13, 1975, and a bombing on February 26, 1993. In 1998, the Port Authority decided to privatize the World Trade Center, leasing the buildings to a private company to manage, and awarded the lease to Silverstein Properties in July 2001.

On the morning of September 11, 2001, Al-Qaeda-affiliated hijackers flew two Boeing 767 jets into the complex, one into each tower, in a coordinated terrorist attack. After burning for 56 minutes, the South Tower (2) collapsed, followed a half-hour later by the North Tower (1), with the attacks on the World Trade Center resulting in 2,753 deaths.^[7] 7 World Trade Center collapsed later in the day and the other buildings, although they did not collapse, had to be demolished because they were damaged beyond repair. The process of cleanup and recovery at the World Trade Center site took eight months. The first new building at the site was 7 World Trade Center, which opened in May 2006. The Lower Manhattan Development Corporation (LMDC), established in November 2001 to oversee the rebuilding process, organized competitions to select a site plan and memorial design. Memory Foundations, designed by Daniel Libeskind, was selected as the master plan, but this went through substantial changes in design. The new World Trade Center complex will include One World Trade Center, three other high-rise office towers, and the National September 11 Memorial & Museum.

Planning and construction[link]

The idea of establishing a World Trade Center in New York City was first proposed in 1943. The New York State Legislature passed a bill authorizing New York Governor Thomas E. Dewey to begin developing plans for the project^[8] but the plans were put on hold in 1949.^[9] During the late 1940s and 1950s, economic growth in New York City was concentrated in Midtown Manhattan, while Lower Manhattan was left out. To help stimulate urban renewal, David Rockefeller suggested that the Port Authority build a World Trade Center in Lower Manhattan.^[10]

Initial plans, made public in 1961, identified a site along the East River for the World Trade Center.^[11] As a bi-state agency, the Port Authority required approval for new projects from the governors of both New York and New Jersey. New Jersey Governor Robert B. Meyner objected to New York getting a $335 million project.^[12] Toward the end of 1961, negotiations with outgoing New Jersey Governor Meyner reached a stalemate.^[13]

At the time, ridership on New Jersey's Hudson and Manhattan Railroad (H&M) had declined substantially from a high of 113 million riders in 1927 to 26 million in 1958 after new automobile tunnels and bridges had opened across the Hudson River.^[14] In a December 1961 meeting between Port Authority director Austin J. Tobin and newly elected New Jersey Governor Richard J. Hughes, the Port Authority offered to take over the Hudson & Manhattan Railroad to have it become the Port Authority Trans-Hudson (PATH). The Port Authority also decided to move the World Trade Center project to the Hudson Terminal building site on the west side of Lower Manhattan, a more convenient location for New Jersey commuters arriving via PATH.^[13] With the new location and Port Authority acquisition of the H&M Railroad, New Jersey, agreed to support the World Trade Center project.^[15]

Approval was also needed from New York City Mayor John Lindsay and the New York City Council. Disagreements with the city centered on tax issues. On August 3, 1966, an agreement was reached that the Port Authority would make annual payments to the City in lieu of taxes for the portion of the World Trade Center leased to private tenants.^[16] In subsequent years, the payments would rise as the real estate tax rate increased.^[17]

Architectural design[link]

On September 20, 1962, the Port Authority announced the selection of Minoru Yamasaki as lead architect and Emery Roth & Sons as associate architects.^[18] Yamasaki devised the plan to incorporate twin towers; Yamasaki's original plan called for the towers to be 80 stories tall.^[19] To meet the Port Authority's requirement for 10,000,000 square feet (930,000 m²)) of office space, the buildings would each have to be 110 stories tall.^[20]

A typical floor layout and elevator arrangement of the WTC towers.

A major limiting factor in building height is the issue of elevators; the taller the building, the more elevators are needed to service the building, requiring more space-consuming elevator banks.^[20] Yamasaki and the engineers decided to use a new system with two "sky lobbies"—floors where people could switch from a large-capacity express elevator to a local elevator that goes to each floor in a section. This allowed the design to stack local elevators within the same elevator shaft. Located on the 44th and 78th floors of each tower, the sky lobbies enabled the elevators to be used efficiently, increasing the amount of usable space on each floor from 62 to 75 percent by reducing the number of elevator shafts.^[21][22] Altogether, the World Trade Center had 95 express and local elevators.^[23] This system was inspired by the New York City Subway system whose lines include express stations where both express and local trains stop and local stations where only local trains stop.^[24]

Yamasaki's design for the World Trade Center, unveiled to the public on January 18, 1964, called for a square plan approximately 208 feet (63 m) in dimension on each side.^[19][25] The buildings were designed with narrow office windows 18 inches (46 cm) wide, which reflected Yamasaki's fear of heights as well as his desire to make building occupants feel secure.^[26] Yamasaki's design included building facades sheathed in aluminum-alloy.^[27] The World Trade Center was one of the most-striking American implementations of the architectural ethic of Le Corbusier, and it was the seminal expression of Yamasaki's gothic modernist tendencies.^[28]

In addition to the twin towers, the plan for the World Trade Center complex included four other low-rise buildings, which were built in the early 1970s. The 47-story 7 World Trade Center building was added in the 1980s, to the north of the main complex. Altogether, the main World Trade Center complex occupied a 16-acre (65,000 m²) superblock.^[29]

Structural design[link]

The World Financial Center and Battery Park City were built on reclaimed land.

The structural engineering firm Worthington, Skilling, Helle & Jackson worked to implement Yamasaki's design, developing the tube-frame structural system used in the twin towers. The Port Authority's Engineering Department served as foundation engineers, Joseph R. Loring & Associates as electrical engineers, and Jaros, Baum & Bolles as mechanical engineers. Tishman Realty & Construction Company was the general contractor on the World Trade Center project. Guy F. Tozzoli, director of the World Trade Department at the Port Authority, and Rino M. Monti, the Port Authority's Chief Engineer, oversaw the project.^[30] As an interstate agency, the Port Authority was not subject to local laws and regulations of the City of New York including building codes. Nonetheless, the structural engineers of the World Trade Center ended up following draft versions of the new 1968 building codes.^[31] The tube-frame design, earlier introduced by Fazlur Khan, was a new approach that allowed more open floor plans than the traditional design that distributed columns throughout the interior to support building loads. The World Trade Center towers used high-strength, load-bearing perimeter steel columns called Vierendeel trusses that were spaced closely together to form a strong, rigid wall structure, supporting virtually all lateral loads such as wind loads, and sharing the gravity load with the core columns. The perimeter structure containing 59 columns per side was constructed with extensive use of prefabricated modular pieces each consisting of three columns, three stories tall, connected by spandrel plates.^[31] The spandrel plates were welded to the columns to create the modular pieces off-site at the fabrication shop.^[32] Adjacent modules were bolted together with the splices occurring at mid-span of the columns and spandrels. The spandrel plates were located at each floor, transmitting shear stress between columns, allowing them to work together in resisting lateral loads. The joints between modules were staggered vertically so the column splices between adjacent modules were not at the same floor.^[31]

The core of the towers housed the elevator and utility shafts, restrooms, three stairwells, and other support spaces. The core of each tower was a rectangular area 87 by 135 feet (27 by 41 m) and contained 47 steel columns running from the bedrock to the top of the tower. The large, column-free space between the perimeter and core was bridged by prefabricated floor trusses. The floors supported their own weight as well as live loads, providing lateral stability to the exterior walls and distributing wind loads among the exterior walls.^[33] The floors consisted of 4 inches (10 cm) thick lightweight concrete slabs laid on a fluted steel deck. A grid of lightweight bridging trusses and main trusses supported the floors.^[34] The trusses connected to the perimeter at alternate columns and were on 6 foot 8 inch (2.03 m) centers. The top chords of the trusses were bolted to seats welded to the spandrels on the exterior side and a channel welded to the core columns on the interior side. The floors were connected to the perimeter spandrel plates with viscoelastic dampers that helped reduce the amount of sway felt by building occupants.

Hat trusses (or "outrigger truss") located from the 107th floor to the top of the buildings were designed to support a tall communication antenna on top of each building.^[34] Only 1 WTC (north tower) actually had an antenna fitted; it was added in 1978.^[35] The truss system consisted of six trusses along the long axis of the core and four along the short axis. This truss system allowed some load redistribution between the perimeter and core columns and supported the transmission tower.^[34]

The tube frame design using steel core and perimeter columns protected with sprayed-on fire resistant material created a relatively lightweight structure that would sway more in response to the wind compared to traditional structures such as the Empire State Building that have thick, heavy masonry for fireproofing of steel structural elements.^[36] During the design process, wind tunnel tests were done to establish design wind pressures that the World Trade Center towers could be subjected to and structural response to those forces.^[37] Experiments also were done to evaluate how much sway occupants could comfortably tolerate, however, many subjects experienced dizziness and other ill effects.^[38] One of the chief engineers Leslie Robertson worked with Canadian engineer Alan G. Davenport to develop viscoelastic dampers to absorb some of the sway. These viscoelastic dampers, used throughout the structures at the joints between floor trusses and perimeter columns along with some other structural modifications, reduced the building sway to an acceptable level.^[39]

Construction[link]

This portion of Cortlandt Street (shown in 1936) was acquired and demolished.

In March 1965, the Port Authority began acquiring property at the World Trade Center site.^[40] Demolition work began on March 21, 1966, to clear thirteen square blocks of low rise buildings in Radio Row for construction of the World Trade Center.^[41] Groundbreaking for the construction of the World Trade Center took place on August 5, 1966.^[42]

The site of the World Trade Center was located on landfill with the bedrock located 65 feet (20 m) below.^[43] To construct the World Trade Center, it was necessary to build a "bathtub" with a slurry wall around the West Street side of the site, to keep water from the Hudson River out.^[44] The slurry method selected by Port Authority's chief engineer, John M. Kyle, Jr., involved digging a trench, and as excavation proceeded, filling the space with a "slurry" mixture composed of bentonite and water, which plugged holes and kept groundwater out. When the trench was dug out, a steel cage was inserted and concrete was poured in, forcing the "slurry" out. It took fourteen months for the slurry wall to be completed; it was necessary before excavation of material from the interior of the site could begin.^[45] The 1.2 million cubic yards (917,000 m³) of material excavated were used (along with other fill and dredge material) to expand the Manhattan shoreline across West Street to form Battery Park City.^[46][47]

World Trade Center under construction in 1971

The World Trade Center from the then newly completed West Side Highway in July 2001.

In January 1967, the Port Authority awarded $74 million in contracts to various steel suppliers, and Karl Koch was hired to erect the steel.^[48] Tishman Realty & Construction was hired in February 1967 to oversee construction of the project.^[49] Construction work began on the North Tower in August 1968; construction on the South Tower was underway by January 1969.^[50] The original Hudson Tubes, carrying PATH trains into Hudson Terminal, remained in service as elevated tunnels during the construction process until 1971 when a new PATH station opened.^[51]

The topping out ceremony of 1 WTC (North Tower) took place on December 23, 1970, while 2 WTC's ceremony (South Tower) occurred later on July 19, 1971.^[50] The first tenants moved into the North Tower in December 1970; the South Tower accepted tenants in January 1972.^[52] When the World Trade Center twin towers were completed, the total costs to the Port Authority had reached $900 million.^[53] The ribbon cutting ceremony was on April 4, 1973.^[54]

Criticism[link]

Plans to build the World Trade Center were controversial. The site for the World Trade Center was the location of Radio Row, home to hundreds of commercial and industrial tenants, property owners, small businesses, and approximately 100 residents, many of whom fiercely resisted forced relocation.^[55] A group of small businesses affected filed an injunction challenging the Port Authority's power of eminent domain.^[56] The case made its way through the court system to the United States Supreme Court; the Court refused to accept the case.^[57]

Private real estate developers and members of the Real Estate Board of New York, led by Empire State Building owner Lawrence A. Wien, expressed concerns about this much "subsidized" office space going on the open market, competing with the private sector when there was already a glut of vacancies.^[58][59] Others questioned whether the Port Authority really ought to take on a project described by some as a "mistaken social priority".^[60]

The World Trade Center design brought criticism of its aesthetics from the American Institute of Architects and other groups.^[27][61] Lewis Mumford, author of The City in History and other works on urban planning, criticized the project and described it and other new skyscrapers as "just glass-and-metal filing cabinets".^[62] The twin towers' narrow office windows, only 18 inches (46 cm) wide, were disliked by many for impairing the view from the buildings.^[26]

The trade center's "superblock", replacing a more traditional, dense neighborhood, was regarded by some critics as an inhospitable environment that disrupted the complicated traffic network typical of Manhattan. For example, in his book The Pentagon of Power, Lewis Mumford denounced the center as an "example of the purposeless giantism and technological exhibitionism that are now eviscerating the living tissue of every great city".^[63]

For many years, the immense Austin J. Tobin Plaza was often beset by brisk winds at ground level.^[64] In 1999, the outdoor plaza reopened after undergoing $12 million renovations, which involved replacing marble pavers with gray and pink granite stones, adding new benches, planters, new restaurants, food kiosks and outdoor dining areas.^[65]

Complex[link]

North and South towers[link]

The WTC site building arrangement

With the construction of 7 World Trade Center in the 1980s, the World Trade Center had a total of seven buildings, but the most notable were the main two towers. Each stood over 1,350 feet (410 m) high, and occupied about one acre (43,560 square feet) of the total 16 acres (65,000 m²) of the site's land. During a press conference in 1973, Yamasaki was asked, "Why two 110-story buildings? Why not one 220-story building?" His response was: "I didn't want to lose the human scale."^[66]

When completed in 1972, 1 World Trade Center (the North Tower) became the tallest building in the world for two years, surpassing the Empire State Building after a 40-year reign. The North Tower stood 1,368 feet (417 m) tall and featured a telecommunications antenna or mast that was added at the top of the roof in 1978 and stood 360 feet (110 m) tall. With the 360-foot (110 m)-tall antenna/mast, the highest point of the North Tower reached 1,728 ft (527 m). 2 World Trade Center (the South Tower) became the second tallest building in the world when completed in 1973. The South Tower's rooftop observation deck was 1,362 ft (415 m) high and its indoor observation deck was 1,310 ft (400 m) high.^[67] The World Trade Center towers held the height record only briefly: Chicago's Sears Tower, finished in May 1973, reached 1,450 feet (440 m) at the rooftop.^[68] Throughout their existence, however, the WTC towers had more floors (at 110) than any other building. This number was not surpassed until the advent of the Burj Khalifa, which opened in 2010.

Of the 110 stories, eight were set aside for technical services in mechanical floors Level B5/B6 (floors 7/8, 41/42, 75/76, and 108/109), which are four two-floor areas that evenly spaced up the building. All the remaining floors were free for open-plan offices. Each floor of the towers had 40,000 square feet (3,700 m²) of space for occupancy.^[23] Each tower had 3,800,000 square feet (350,000 m²) of office space. Altogether the entire complex of seven buildings had 11,200,000 square feet (1,040,000 m²) of space.

Lobby of Tower 1, looking south along the east side of the building

Initially conceived as a complex dedicated to companies and organizations directly taking part in "world trade", they at first failed to attract the expected clientele. During the early years, various governmental organizations became key tenants of the World Trade Center including the State of New York. It was not until the 1980s that the city's perilous financial state eased, after which an increasing number of private companies—mostly financial firms tied to Wall Street—became tenants. During the 1990s, approximately 500 companies had offices in the complex including many financial companies such as Morgan Stanley, Aon Corporation, Salomon Brothers and the Port Authority itself. The basement concourse of the World Trade Center included The Mall at the World Trade Center along with a PATH station.^{[citation needed]} The North Tower became the home of the corporate headquarters of Cantor Fitzgerald,^[69] and it also became the headquarters of the Port Authority of New York and New Jersey.^[70]

Electrical service to the towers was supplied by Consolidated Edison (ConEd) at 13,800 volts. This service passed through the World Trade Center Primary Distribution Center (PDC) and sent up through the core of the building to electrical substations located on the mechanical floors. The substations "stepped" the 13,800 primary voltage down to 480/277 volt secondary power and further to 120/208 volt general power and lighting service. The complex also was served by emergency generators located in the sublevels of the towers and on the roof of 5 WTC.^[71][72]

The 110th floor of 1 World Trade Center (the North Tower) housed radio and television transmission equipment. The roof of 1 WTC contained a vast array of transmission antennas including the 360 ft (approx 110 m) center antenna mast, rebuilt in 1999 by Dielectric Inc. to accommodate DTV. The center mast contained the television signals for almost all NYC television broadcasters: WCBS-TV 2, WNBC-TV 4, WNYW 5, WABC-TV 7, WWOR-TV 9 Secaucus, WPIX 11, WNET 13 Newark, WPXN-TV 31 and WNJU 47 Linden. It also had four NYC FM broadcasters: WPAT-FM 93.1, WNYC 93.9, WKCR 89.9, and WKTU 103.5. Access to the roof was controlled from the WTC Operations Control Center (OCC) located in the B1 level of 2 WTC.

Top of the World observation deck[link]

Two World Trade Center's observation deck received an estimated 80,000 visitors a day.

Although most of the space in the World Trade Center complex was off-limits to the public, the South Tower featured an indoor and outdoor public observation area called Top of the World Trade Center Observatories on its 107th and 110th floors. Visitors would pass through security checks added after the 1993 World Trade Center bombing,^[73] then were whisked to the 107th floor indoor observatory at a height of 1,310 feet (400 m). The columns on each face of the building were narrowed on this level to allow 28 inches of glass between them. The Port Authority renovated the observatory in 1995, then leased it to Ogden Entertainment to operate. Attractions added to the observation deck included a simulated helicopter ride around the city. The 107th floor food court was designed with a subway car theme and featured Sbarro and Nathan's Famous Hot Dogs.^[74][75] Weather permitting, visitors could take two short escalator rides up from the 107th floor viewing area to an outdoor viewing platform on the 110th floor at a height of 1,377 ft (420 m).^[76] On a clear day, visitors could see up to 50 miles (80 km).^[74] An anti-suicide fence was placed on the roof itself, with the viewing platform set back and elevated above it, requiring only an ordinary railing and leaving the view unobstructed, unlike the observation deck of the Empire State Building.^[75]

Windows on the World restaurant[link]

The North Tower had a restaurant on its 106th and 107th floors called Windows on the World, which opened in April 1976. The restaurant was developed by Joe Baum at a cost of more than $17 million.^[77] Aside from the main restaurant, two offshoots were located at the top of the North Tower: "Hors d'Oeuvrerie" (offered a Danish smorgasbord during the day and sushi in the evening) and "Cellar in the Sky" (a small wine bar).^[78] Windows on the World also had a wine school program run by Kevin Zraly. Windows on the World was closed following the 1993 World Trade Center bombing.^[77] Upon reopening in 1996, Hors d'Oeuvrerie and Cellar in the Sky were replaced with the "Greatest Bar on Earth" and "Wild Blue".^[78] In 2000, its last full year of operation, Windows on the World reported revenues of $37 million, making it the highest-grossing restaurant in the United States.^[79] The Skydive Restaurant, opened in 1976 on the 44th floor of the North Tower, was also operated by Windows on the World restaurant, but served only lunch.

Other buildings[link]

Five smaller buildings stood around the 16 acres (65,000 m²) block. One was the 22-floor hotel, which opened in 1981 as the Vista Hotel, and in 1995 became the Marriott World Trade Center (3 WTC) at the southwest corner of the site. Three low-rise buildings (4 WTC, 5 WTC, and 6 WTC) in the same hollow tube design as the towers also stood around the plaza. 6 World Trade Center, at the northwest corner, housed the United States Customs Service and the U.S. Commodities Exchange. 5 World Trade Center was located at the northeast corner above the PATH station and 4 World Trade Center was at the southeast corner. In 1987, a 47-floor office building called 7 World Trade Center was built north of the block. Beneath the World Trade Center complex was an underground shopping mall, which in turn had connections to various mass transit facilities including the New York City Subway system and the Port Authority's own PATH trains connecting Manhattan to Jersey City, Hoboken, and Newark.

One of the world's largest gold depositories was stored underneath the World Trade Center, owned by a group of commercial banks. The 1993 bomb detonated close by the vault held. Seven weeks after the September 11 attacks, $230 million in precious metals was removed from basement vaults of 4 WTC, which included 3,800 100-Troy-ounce registered gold bars and 30,000 1,000-ounce silver bars.^[80]

Life and events[link]

On a typical weekday 50,000 people worked in the towers^[81] with another 200,000 passing through as visitors.^[82] The complex was so large that it had its own zip code: 10048.^[83] The towers offered expansive views from the observation deck atop the South Tower and the Windows on the World restaurant on top of the North Tower. The Twin Towers became known worldwide, appearing in numerous movies and television shows as well as on postcards and other merchandise, and became seen as a New York icon, in the same league as the Empire State Building, Chrysler Building and the Statue of Liberty.^[84]

French high wire acrobatic performer Philippe Petit walked between the towers on a tightrope in 1974, as shown in the documentary film Man on Wire.^[85]

Brooklyn toymaker George Willig scaled the exterior of the south tower in 1977.^[86] In 1983, on Memorial Day, high-rise firefighting and rescue advocate Dan Goodwin successfully climbed the outside of the WTC's North Tower. His stunt was meant to call attention to the inability to rescue people potentially trapped in the upper floors of skyscrapers.^[87][88]

The 1995 PCA world chess championship was played on the 107th floor of the South Tower.^[89]

In January 1998, Mafia member Ralph Guarino, who had gained maintenance access to the World Trade Center, arranged a three-man crew for a heist that netted over $2 million from a Brinks delivery to the eleventh floor of the World Trade Center.^[90]

February 13, 1975 fire[link]

On February 13, 1975, a three-alarm fire broke out on the 11th floor of the North Tower. Fire spread through the core to the 9th and 14th floors by igniting the insulation of telephone cables in a utility shaft that ran vertically between floors. Areas at the furthest extent of the fire were extinguished almost immediately and the original fire was put out in a few hours. Most of the damage was concentrated on the 11th floor, fueled by cabinets filled with paper, alcohol-based fluid for office machines, and other office equipment. Fireproofing protected the steel and there was no structural damage to the tower. Other than the damage caused by the fire, a few floors below suffered water damage from the extinguishing of the fires above. At that time, the World Trade Center had no fire sprinkler systems.^[91][92]

February 26, 1993 bombing[link]

Underground bombing.

On February 26, 1993, at 12:17 p.m., a Ryder truck filled with 1,500 pounds (680 kg) of explosives, planted by Ramzi Yousef, detonated in the underground garage of the North Tower.^[93] The blast opened a 100 foot (30 m) hole through five sublevels with the greatest damage occurring on levels B1 and B2 and significant structural damage on level B3.^[94] Six people were killed and 50,000 other workers and visitors were left gasping for air within the 110 story towers. Many people inside the North Tower were forced to walk down darkened stairwells that contained no emergency lighting, some taking two hours or more to reach safety.^[95][96]

Yousef fled to Pakistan after the bombing but was arrested in Islamabad in February 1995, and was extradited back to the United States to face trial.^[97] Sheikh Omar Abdel Rahman was convicted in 1996 for involvement in the bombing and other plots.^[98] Yousef and Eyad Ismoil were convicted in November 1997 for their carrying out the bombing.^[99] Four others had been convicted in May 1994 for their involvement in the 1993 bombing.^[100] According to a presiding judge, the conspirators' chief aim at the time of the attack was to destabilize the north tower and send it crashing into the south tower, toppling both landmarks.^[101]

Following the bombing, floors that were blown out needed to be repaired to restore the structural support they provided to columns.^[102] The slurry wall was in peril following the bombing and loss of the floor slabs that provided lateral support against pressure from Hudson River water on the other side. The refrigeration plant on sublevel B5, which provided air conditioning to the entire World Trade Center complex, was heavily damaged.^[103] Subsequent to the bombing, the Port Authority installed photoluminescent markings in the stairwells.^[104] The fire alarm system for the entire complex needed to be replaced because critical wiring and signaling in the original system was destroyed.^[105] As a memorial to the victims of the bombing of the tower, a reflecting pool was installed with the names of those who had been killed in the blast.^[106] However, the memorial was destroyed following the September 11 attacks. Names of the victims of the 1993 bombing are included in the National September 11 Memorial & Museum.

Lease[link]

In 1998, the Port Authority approved plans to privatize the World Trade Center.^[107] In 2001, the Port Authority sought to lease the World Trade Center to a private entity. Bids for the lease came from Vornado Realty Trust, a joint bid between Brookfield Properties Corporation and Boston Properties,^[108] and a joint bid by Silverstein Properties and The Westfield Group.^[109] By privatizing the World Trade Center, it would be added to the city's tax rolls^[109] and provide funds for other Port Authority projects.^[110] On February 15, 2001, the Port Authority announced that Vornado Realty Trust had won the lease for the World Trade Center, paying $3.25 billion for the 99-year lease.^[111] Vornado outbid Silverstein by $600 million though Silverstein upped his offer to $3.22 billion. However, Vornado insisted on last minute changes to the deal, including a shorter 39-year lease, which the Port Authority considered nonnegotiable.^[112] Vornado later withdrew and Silverstein's bid for the lease to the World Trade Center was accepted on April 26, 2001,^[113] and closed on July 24, 2001.^[114]

Destruction[link]

United Airlines Flight 175 hits the south tower

On September 11, 2001, terrorists hijacked American Airlines Flight 11 and crashed it into the northern façade of the north tower at 8:46 a.m., the aircraft striking between the 93rd and 99th floors. Seventeen minutes later, at 9:03 a.m., a second team of terrorists crashed the similarly hijacked United Airlines Flight 175 into the south tower, striking it between the 77th and 85th floors.^[115] The damage caused to the north tower by Flight 11 destroyed any means of escape from above the impact zone, trapping 1,344 people.^[116] Flight 175 had a much more off-centered impact compared to Flight 11, and a single stairwell was left intact; however, only a few people managed to pass through it successfully before the tower collapsed. Although the south tower was struck lower than the north tower, thus affecting more floors, a smaller number, fewer than 700, were killed instantly or trapped.^[117]

At 9:59 a.m., the South Tower collapsed after burning for approximately 56 minutes. The fire caused steel structural elements, already weakened from the plane impact, to fail. The north tower collapsed at 10:28 a.m., after burning for approximately 102 minutes.^[118] At 5:20 p.m.^[119] on September 11, 2001, 7 World Trade Center started to collapse with the crumble of the east penthouse, and it collapsed completely at 5:21 p.m.^[119] owing to uncontrolled fires causing structural failure.^[120] This account of the collapse's cause was disputed by proponents of World Trade Center controlled demolition conspiracy theories.

The 3 World Trade Center, a Marriott hotel, was destroyed during the collapse of the two towers. The three remaining buildings in the WTC plaza sustained heavy damage from debris and were ultimately demolished.^[121] The Deutsche Bank Building across Liberty Street from the World Trade Center complex was later condemned owing to the uninhabitable toxic conditions inside; it was deconstructed, with work completed in early 2011.^[122][123] The Borough of Manhattan Community College's Fiterman Hall at 30 West Broadway was also condemned owing to extensive damage in the attacks and is slated for deconstruction.^[124]

The World Trade Center on fire with the Statue of Liberty in the foreground

In the immediate aftermath of the attacks, media reports suggested that tens of thousands might have been killed in the attacks, as on any given day over 50,000 people could be inside the towers. Ultimately, 2,753 death certificates (excluding those for hijackers) were filed relating to the 9/11 attacks, including one filed for Felicia Dunn-Jones, who was added to the official death toll in May 2007; Dunn-Jones died five months later from a lung condition linked to exposure to dust during the collapse of the World Trade Center.^[125] Three other victims were then added to the official death toll by the city medical examiner's office: Dr. Sneha Anne Philip, who was last seen the day before the attacks; Leon Heyward, a man who developed lymphoma and subsequently died in 2008 as a result of dust ingestion during the events following the attacks to the Twin Towers;^[126][127] and Jerry Borg, who died in December 2010 of pulmonary sarcoidosis determined in June 2011 to be the result of dust from the attacks.^[7] Cantor Fitzgerald L.P., an investment bank on the 101st–105th floors of One World Trade Center, lost 658 employees, considerably more than any other employer,^[128] while Marsh & McLennan Companies, located immediately below Cantor Fitzgerald on floors 93–101 (the location of Flight 11's impact), lost 295 employees, and 175 employees of Aon Corporation were killed.^[129] In addition, 343 of the dead were New York City firefighters, 84 were Port Authority employees, of whom 37 were members of the Port Authority Police Department, and another 23 were New York City Police Department officers.^{[130][131][132]} Ten years after the attacks, only 1,629 victims have been positively identified.^[133] Of all the people who were still in the towers when they collapsed, only 20 were pulled out alive. PAPD Officers William Jimeno and Sgt. John McLoughlin were survivors 18 and 19.^[134]

Rebuilding[link]

After years of delay and controversy, reconstruction at the World Trade Center site is now well underway. The new complex will include One World Trade Center (formerly known as the Freedom Tower), 7 World Trade Center, three other high-rise office buildings, a museum and memorial, and a transportation hub similar in size to Grand Central Terminal. Both One and Four World Trade Center are on track for completion and occupancy by 2013.^[135][136] The 9/11 memorial is complete, with the museum set to open in 2012.^[137] Two and Three World Trade Center, as well as the Transportation Hub, are also making progress, set to be finished by around 2015.