About the Original Twin Towers at the World Trade Center, 1973-2001

Designed for Strength, Demolished by Terrorists on September 11, 2001

Looking over water at a Skyline of New York City and two tall rectangular towers
Twin Towers Dominate the Skyline of New York City. Fotosearch/Getty Images

Designed by American architect Minoru Yamasaki (1912-1986), the original World Trade Center from 1973 consisted of two 110-story buildings (known as the "twin towers") and five smaller buildings. Yamasaki studied over a hundred models before adopting the twin tower design. Plans for a single tower were rejected because the size was thought to be cumbersome and impractical back in the 1960s. Plans for several towers "looked too much like a housing project," Yamasaki said. This retrospective shows how the original twin towers were designed for peace and strength before being demolished by terrorists on September 11, 2001.

About the World Trade Center in New York City

detail of metal lattice on skyscraper
Aluminum and Steel Lattice Tridents. Wolfgang Meier/Getty Images (cropped)

What became known as the "tridents" are the recognizable remains of the twin towers.

After the September 11 terrorist attacks, two trident (3-pronged) columns from the original twin towers were salvaged from the ruins. They became part of the exhibition at the National 9/11 Museum at ground zero.

Engineers helped us understand why the twin towers collapsed the way they did. The tridents were part of a tubular framework. Lead structural engineer Leslie E. Robertson explained that the architect Minoru Yamasaki proposed narrow windows "to give people a sense of security as they looked down from on high." Others have said that Yamasaki himself was afraid of heights, and that accounted for the narrow windows. "Our contribution," Robertson reflected, "was to make the closely spaced columns the fundamental lateral-force resisting system for the two towers." The aluminum-clad prefabricated steel framework withstood even the lateral "impact loads imposed on September 11." The tubular frame allowed a lightweight building with open interior office spaces. The natural sway of the tall buildings was mitigated not by heavy steel reinforeced with concrete, but by engineered dampers that acted like shock absorbers.

The World Trade Center twin towers were light, economical structures designed to keep the wind bracing on the outside surfaces.

Architect Yamasaki presented the plan in January 1964, and excavation began by August 1966. The steel construction started two years later, in August 1968. The north tower (WTC 1) was finished in 1970 and the south tower (WTC 2) was completed in 1972, with a dedication ceremony on April 4, 1973. "The World Trade Center is a living symbol of man's dedication to world peace," said the architect at the opening ceremony.

The first terrorist attack on February 26, 1993 was a truck bomb in the underground parking of the north tower. The second terrorist attack on September 11, 2001 was with two hijacked commercial airliners each flying into a tower.

The WTC and Structure of the Twin Towers

Two workers having a break on the south tower of the world trade center in New York City in summer 1998
Top of the North Tower. David Bank/Getty Images (cropped)

The first skyscraper to be completed was Tower One, the north tower, in 1970. At 1,368 feet (414 meters) tall, it rose an incredible 110 stories. A 360-foot television tower was installed on the north tower in June 1980. Tower Two, the south tower, was 1,362 feet (412 meters) tall, but still 110 stories high.

The five other buildings on the World Trade Center site were much smaller: WTC 3 was a 22-floor hotel; WTC 4, the South Plaza Building, had 9 floors; WTC 5, the North Plaza Building, had 9 floors; WTC 6, the United States Customs House, had 8 floors; and WTC 7, completed in 1987, was 47 floors high. The World Trade Center construction site closed off one of New York City's north-south streets in 1967 — Greenwich Street in Manhattan — to accommodate the proposed seven buildings:

Each of the twin towers was 64 meters square. Each tower rested on solid bedrock, the foundations extending 70 feet (21 meters) below grade. The height-to-width ratio was 6.8.

The facades of the twin towers were constructed of aluminum and steel lattice, built of a lightweight tube construction with 244 closely spaced columns on the outer walls and no interior columns in office spaces. An 80-centimeter tall web joist connected the core to the perimeter at each floor. Concrete slabs were poured over the web joists to form the floors. Both Towers weighed about 1,500,000 tons together.

Each tower contained 104 passenger elevators for the 50,000 people who worked there. Each Tower had 21,800 windows — over 600,000 square feet of glass.

During peak construction between 1966 and 1973; 3,500 people worked at the site — 60 people died during construction.

In rebuilding the World Trade Center site after 9/11, architects paid homage to the lost twin towers by giving the new skyscraper, One World Trade Center, similar dimensions. Measuring 200 feet square, the footprint of One World Trade Center matches each of the twin towers. Except for the spire, the 2014 One World Trade Center is 1,368 feet tall, like the north tower. If you also exclude the parapet, One World Trade Center is 1,362 feet tall, like Tower Two.

The World Trade Center towers were among the tallest buildings in the world and contained nine million square feet of office space. The chosen design architects were Minoru Yamasaki Associates, from Rochester Hills, Michigan. The local architectural firm overseeing the design was Emery Roth & Sons of New York. The foundation engineers came from the Port Authority of New York and New Jersey Engineering Department.

World Trade Center Plaza

round metal sculpture on the plaza in front of trident lattice of tall building
Sphere Sculpture by Fritz Koenig Between Twin Towers at World Trade Center Plaza. Robert J Fisch/Getty Images (cropped)

After the twin towers were complete, 250,000 gallons of paint were used to maintain the towers each year. Almost the same number of murders (19) were committed at the WTC as babies born there (17).

The twin towers were not the highest skyscrapers in America — the 1973 Willis Tower in Chicago took that honor — but they were taller than the Empire State Building and became the focus of 1970s stunts and popular culture. On August 7, 1974 Philippe Petit used a bow and arrow to assemble a steel cable between the two towers and then he walked across the tightrope. Other stunts included parachuting from the top and climbing from the bottom of the towers. In 1976, the 1933 film where King Kong climbed the Empire State Building was remade with the monster in Lower Manhattan, climbing one tower and leaping to another before his inevitable fall.

The Sphere, a 25-foot bronze sculpture by German artist Fritz Koenig (1924-2017), was commissioned in 1966 and stood on the plaza between the twin towers from 1971 until the terrorist attacks nearly destroyed it. Damaged but basically intact, the 25-ton sculpture was moved to Battery Park as a memorial and symbol of American persistence. In 2017, the sculpture was moved to Liberty Park overlooking the 9/11 Memorial Plaza.

The Buildings We Build

Views of the World Trade Center (both of its twin towers still under construction) and Manhattan skyline views taken from New Jersey shore
Twin Towers Under Construction. Bettmann/Getty Images (cropped)

The 16 acre area in Lower Manhattan was meant to be an homage to capitalism and the "center" of "world trade." David Rockefeller had originally proposed developing along the East River, but the West side was chosen — disregarding the protests of displaced businesses bought out by eminent domain. The tall skyscrapers for New York's Financial District would replace the many small businesses that made up "Radio Row" electronics shops. Greenwich Street would be chopped off, disconnecting city neighborhoods largely populated by immigrants from the Middle East, including Syria.

Thousands of construction workers tore down the small businesses and built the World Trade Center superblock beginning in 1966. A 1986 documentary, Building the World Trade Center, by the Port Authority of New York and New Jersey is testament to the architecture, construction, and development process.

The chosen design architect, Minoru Yamasaki, may have been conflicted by the values and politics surrounding the vast, high-profile project. The architect Paul Heyer quotes Yamasaki as saying:

"There are a few very influential architects who sincerely believe that all buildings must be 'strong'. The word 'strong' in this context seems to connote 'powerful' — that is, each building should be a monument to the virility of our society. These architects look with derision upon attempts to build a friendly, more gentle kind of building. The basis for their belief is that our culture is derived primarily from Europe, and that most of the important traditional examples of European architecture are monumental, reflecting the need of the state, church, or the feudal families — the primary patrons of these buildings — to awe and impress the masses. This is incongruous today. Although it is inevitable for architects who admire these great monumental buildings of Europe to strive for the quality most evident in them — grandeur, the elements of mysticism and power, basic to cathedrals and palaces, are also incongruous today, because the buildings we build for our times are for a totally different purpose."

Yamasaki, the World Trade Center, and World Peace

low-angle view of two rectangular skyscrapers near each other
Twin Towers, Symbols of Peace. Comstock/Getty Images (cropped)

Architect Minoru Yamasaki rejected the European notion of a strong, powerful, monumental architecture. The buildings we build today "are for a totally different purpose," he has said. At the opening of the World Trade Center on April 4, 1973, Yamasaki told the crowd that his skyscrapers were symbols of peace:

"I feel this way about it. World trade means world peace and consequently the World Trade Center buildings in New York...had a bigger purpose than just to provide room for tenants. The World Trade Center is a living symbol of man's dedication to world peace...beyond the compelling need to make this a monument to world peace, the World Trade Center should, because of its importance, become a representation of man's belief in humanity, his need for individual dignity, his beliefs in the cooperation of men, and through cooperation, his ability to find greatness."


  • Office of Cultural Education, New York State Education Department (NYSED). The World Trade Center Chronology of Construction. http://www.nysm.nysed.gov/wtc/about/construction.html
  • The World Trade Center Facts and Figures, Office of Cultural Education, New York State Education Department (NYSED) at http://www.nysm.nysed.gov/wtc/about/facts.html
  • Leslie E. Robertson. "Reflections on the World Trade Center." The Bridge, Vol. 32, Number 1, Spring 2002, PP. 5-10. http://www.nae.edu/nae/bridgecom.nsf/weblinks/NAEW-63AS9S/$FILE/Bridge-v32n1.pdf
  • Paul Heyer. Architects on Architecture: New Directions in America, Walker, 1966, p. 186