<P> In January 1964, the Port Authority inked a deal with the State of New York to locate government offices at the World Trade Center . The Port Authority began signing commercial tenants in the spring and summer of 1964, including several banks . In 1965, the Port Authority signed the United States Customs Service as a tenant . </P> <P> A final obstacle for the Port Authority was getting approval from New York City Mayor John Lindsay and the New York City Council, who raised concerns about the limited extent that the Port Authority involved the city in the negotiations and deliberations . Negotiations between The City of New York and the Port Authority were centered on tax issues . A final agreement was made on August 3, 1966, 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 . In subsequent years, the payments would rise as the real estate tax rate increased . </P> <P> On September 20, 1962, the Port Authority announced the selection of Minoru Yamasaki as lead architect, and Emery Roth & Sons as associate architects . Originally, Yamasaki submitted to the Port Authority a concept incorporating twin towers, but with each building only 80 stories tall . Yamasaki remarked that the "obvious alternative, a group of several large buildings, would have looked like a housing project ." Yamasaki's design for the World Trade Center was unveiled to the public on January 18, 1964, with an eight - foot model . The towers had a square plan, approximately 207 feet (63 m) in dimension on each side . The buildings were designed with narrow office windows, only 18 inches (45 cm) wide, which reflected on Yamasaki's fear of heights and desire to make building occupants feel secure . Yamasaki's design called for the building facades to be sheathed in aluminum - alloy . </P> <P> To meet the Port Authority's requirement to build 10 million square feet (930,000 m2) of office space, the buildings would each need to be 110 stories tall . A major limiting factor in building heights is elevators; the taller the building, the more elevators are needed to service the building, requiring more space - consuming elevator banks . Yamasaki and the engineers decided to use a new system that included sky lobbies, which are floors where people can switch from a large - capacity express elevator, which goes only to the sky lobbies, to a local elevator that goes to each floor in a section (the local elevators can be stacked 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, while also increasing the amount of usable space on each floor from 62 to 75 percent by reducing the number of required elevator shafts . The World Trade Center towers were the second supertall buildings to use sky lobbies, after the John Hancock Center in Chicago . This system was inspired by the New York City Subway system, whose lines include local stations where local trains stop and express stations where all trains stop . </P>

When was the world trade center first built