<P> The construction of New York City's first World Trade Center complex was conceived as an urban renewal project, spearheaded by David Rockefeller, to help revitalize Lower Manhattan . The project was developed by the Port Authority of New York and New Jersey, which hired architect Minoru Yamasaki who came up with the specific idea for twin towers . After extensive negotiations, the New Jersey and New York state governments, which oversee the Port Authority, agreed to support the World Trade Center project at the Radio Row site on the Lower West Side of Manhattan, New York City . To make the agreement acceptable to New Jersey, the Port Authority agreed to take over the bankrupt Hudson & Manhattan Railroad, which brought commuters from New Jersey to the Lower Manhattan site and, upon the Port Authority's takeover of the railroad, was renamed PATH . </P> <P> The towers were designed as framed tube structures, which provided tenants with open floor plans, uninterrupted by columns or walls . This was accomplished using numerous closely spaced perimeter columns to provide much of the strength to the structure, along with gravity load shared with the core columns . The elevator system, which made use of sky lobbies and a system of express and local elevators, allowed substantial floor space to be freed up for use as office space by making the structural core smaller . The design and construction of the World Trade Center, most centrally its twin towers, involved many other innovative techniques, such as the slurry wall for digging the foundation, and wind tunnel experiments . </P> <P> Construction of the World Trade Center's North Tower began in August 1968, and the South Tower in 1969 . Extensive use of prefabricated components helped to speed up the construction process . The first tenants moved into the North Tower in December 1970 and into the South Tower in January 1972 . Four other low - level buildings were constructed as part of the World Trade Center in the 1970s, and a seventh building was constructed in the mid-1980s . </P> <P> In 1942, Austin J. Tobin became the Executive Director of the Port Authority, beginning a 30 - year career during which he oversaw the planning and development of the World Trade Center . The concept of establishing a "world trade center" was conceived during the post--World War II period, when the United States thrived economically and international trade was increasing . In 1946, the New York State Legislature passed a bill that called for a "world trade center" to be established . The World Trade Corporation was founded, and a board was appointed by New York Governor Thomas E. Dewey to develop plans for the project . Architect John Eberson and his son Drew devised a plan that included 21 buildings over a ten - block area, at an estimated cost of $150 million . In 1949, the World Trade Corporation was dissolved by the New York State Legislature, and plans for a "world trade center" were put on hold . </P>

When did they start building the twin towers