First occupied in 1970, in magnitude and complexity and in pioneering advances in the technology of high-rise buildings, this pair of 110-story buildings was unlike anything constructed before. With almost one full acre on each floor, the project had a gross area of 13 million sf (1.2 million sm) or about 19 times the overall site area of 16 acres. Over 200,000 U.S. tons (182,000 metric tons) of structural steel were required.

The twin towers altered the world of high-rise buildings in many ways not associated directly with structural design. Some of the many facets of the structural system included:
• The use of prefabricated multiple column and spandrel wall panels.
• The use of large, prefabricated floor panels, complete with steel deck and in-floor electrification.
• The World Trade Center provided the first comprehensive environmental and wind tunnel study completed in a boundary layer wind tunnel. The first evaluation of the dynamics of a building in the turbulent wind... the very cornerstone of contemporary design for high-rise buildings.
• The first testing of humans to determine their sensitivity to the lateral oscillation of buildings... thus the first development of rational criteria for the dynamic performance of a high-rise building.
• The development of the concept for "Shaftwall", a lightweight fire-rated wall system that now dominates the construction industry.
• The invention, development and the incorporation of visco-elastic damping units to reduce the swaying motion of a tall building.