Completed in the fall of 1961, architect Eero Saarinen's breathtaking TWA passenger terminal at Idlewild International Airport will stand as a monument to concrete and to the architectural, engineering and construction genius that created it. Of arch cantilever design, the 5,000 ton roof of the great building is of four monolithic concrete shells, flowing out of four sculptured buttresses. Joined integrally at a center plate, the shells vary in thickness from 8 inches at their perimeter to 44 inches at the centerplate. The building is one of the few major contemporary American structures in which all actual structural elements represent the final exterior architectural form. Over two months of study, analysis, and computation preceded actual concrete work on the roof. The final scheme called for initial construction of a center plate that would act as a bulkhead against which to place the four shells and also provide a control station for subsequent concrete operations. When placing began, inspection crews of engineers and carpenters were stationed at key positions under the roof at ground level. Through a system of hanging plumbs, they were able to detect the slightest movement in the formwork and radio so the next bucket load of concrete could be directed for placement at a point that would compensate for the form movement. The next step in construction was the erection of forms for placing the concrete floor. The interior, free of any visible supports, is a two-story building. The building was enclosed so work could continue in the winter.