The new approaches made it possible for the Port Authority to build higher and cheaper, with the twin towers the first skyscrapers to use virtually no masonry in their construction. The changes of this era also allowed the Port Authority to turn far more of the towers over to rentable space—as opposed to safety and service functions, like stairways and elevators—than other skyscrapers. Some of those changes also made escape impossible for people on the upper floors after the attacks of September 11, 2001.
