World Trade Center - Site of the Hudson Terminal Buildings, 1907-1908 by Clinton & Russell. Architects: Minoru Yamasaki and Emery Roth and Sons Completed: 1973-1974

The entire World Trade Center was more than its signature twin towers; it was designed as a complex of seven buildings on 16-acres comprising a city-sized 10 million square feet of rentable office space. The World Trade Center was built and operated by the Port Authority of New York and New Jersey from 1966 to 1974. The Twin Towers, One and Two World Trade Center, represented the ambition of the bi-state authority and of the confident modernism of the late 1960's that saw bigger as better. The World Trade Center replaced the Hudson Terminal Buildings, a pair of 23-story buildings that housed offices as well as a three-level underground commuter rail facility from New Jersey. Dey Street divided the complex into two distinct buildings, which were connected both underground and by a sky-bridge. James Hollis Wells of Clinton and Russell designed the complex for the Hudson and Manhattan Railroad Company. Altogether, the buildings yielded more than 1 million square feet of office space, which made the complex the largest in the world in 1908. The Japanese-born architect Minoru Yamasaki considered more than a hundred different building configurations before settling on the concept of twin towers and three lower-rise structures.

Initially, the towers were to rise 80-90 stories. Only later were they to become the world's tallest man-made structures at 110 stories, following a suggestion said to have originated with the Port Authority's public relations staff. Tower 1 was 1368 feet tall; Tower 2 was 1362 feet. Yamasaki and structural engineer Les Robertson worked closely to create an innovative structural solution, an exterior wall of rigid "hollow tube" construction- closely spaced steel columns with floor trusses extending across to a central core. The columns, clad with a silver-colored aluminum alloy, were 18 3/4" wide and set only 22" apart, making the towers appear from afar to have no windows at all. One World Trade Center was ready for its first tenants in late 1970, even though the final construction on its upper stories were not completed until 1972; Two World Trade Center was finished in 1973. The foundations, which required excavation to bedrock 70 feet below, produced the material for the Battery Park City landfill project in the Hudson River.