The concept of a "world trade center" first surfaced in 1946, when New York's state legislature called for one to bolster the city's role in transatlantic commerce. That early effort collapsed -- projections showed it would only succeed if nearly all of America's largest companies participated. The idea lay dormant until David Rockefeller's Downtown-Lower Manhattan Association proposed a new trade center on the East River waterfront in 1960. But New Jersey Governor Robert B. Meyner balked: why should his state support a $355 million project entirely in New York? Meyner's leverage was the Hudson and Manhattan Railroad, a bankrupt commuter line whose ridership had plummeted from 113 million riders in 1927 to 26 million by 1958. For years, New Jersey had urged the Port Authority to take over the railroad. Now Meyner made it a condition. The deal was struck: the Port Authority would acquire the H&M -- rebranding it PATH -- and build the World Trade Center on the railroad's decrepit Hudson Terminal site on Manhattan's Lower West Side.

The new site covered a roughly trapezoidal twelve-block area bounded by Vesey, Church, Liberty, and West Streets. It was home to Radio Row, a neighborhood of small electronics shops and businesses that had thrived for decades. The Port Authority invoked eminent domain. Merchants fought back, filing injunctions and challenging the project's "public purpose" through the court system all the way to the U.S. Supreme Court. Newspapers published stories about the small-business owners facing eviction. Protesters carried the effigy of a "Mr. Small Businessman" in a mock funeral through the streets. The Port Authority opened a relocation office but insisted on meeting with merchants one by one -- a strategy their de facto spokesperson, Oscar Nadel, recognized as a divide-and-conquer tactic. In April 1963, the New York Court of Appeals upheld the Port Authority's eminent domain power, and the Supreme Court declined to hear an appeal that November. Radio Row was erased to make room for something the world had never seen.

The Port Authority hired architect Minoru Yamasaki, whose only prior high-rise was a 30-story tower in Detroit. When told he had been selected to design a $280 million world trade center, Yamasaki initially thought the offer was a typo. His solution -- twin 110-story towers -- emerged from a practical constraint: the Port Authority mandated 10 million square feet of office space. Spreading that across many buildings would look like a housing project, Yamasaki reasoned. Condensing it into two towers required a revolutionary structural approach. The framed-tube design, drawing on innovations by structural engineer Fazlur Rahman Khan, used closely spaced perimeter steel columns to bear wind and gravity loads, freeing the interior from the forest of columns that cluttered conventional skyscrapers. An elevator system inspired by the New York City Subway -- with local and express stops via sky lobbies -- made 110 floors economically feasible. The design used 40 percent less steel than conventional construction.

Construction of the North Tower began in August 1968, the South Tower in 1969. The foundation work alone was unprecedented: builders excavated to bedrock 65 to 85 feet below street level using a slurry wall technique -- a continuous underground wall of concrete poured into trenches filled with a bentonite slurry to prevent collapse. The excavated material, over a million cubic yards of earth and rock, was used to create new land along the Hudson River waterfront, extending Manhattan's western edge and eventually becoming the site of Battery Park City. The first tenants moved into the North Tower in December 1970. The complex was dedicated on April 4, 1973, and four low-rise buildings were completed around the towers during the early 1970s. A seventh building, 7 World Trade Center, opened in 1987. For a brief period, the twin towers held the title of tallest buildings in the world -- monuments to an era when New York believed it could solve any problem by building bigger.