The terrorist attacks on September 11, 2001, fundamentally shifted the trajectory of skyscraper design and construction, particularly in the United States. The collapse of the World Trade Center towers in New York—then the tallest buildings ever deliberately removed from a skyline—ignited widespread debate about the future of supertall buildings and urban security.
Prior to the attacks, plans were underway for a 2,000-foot Trump Tower in Chicago, with architect Adrian Smith consulting Donald Trump Jr. that very morning. In the wake of the tragedy, the project’s scale was significantly reduced, and detailed designs for the original concept were never made public. Completed in 2009, the Trump International Hotel and Tower in Chicago stands at 1,389 feet including its spire, with the highest occupied floor reaching 1,116 feet, bringing it in line with other city landmarks like the Aon Center and 875 North Michigan Avenue.
At the time of 9/11, the Council for Vertical Urbanism (CVU) recognized just over two dozen “supertall” buildings globally—defined as structures between 984 and 1,965 feet tall—with five located in Chicago, including the Willis Tower (formerly Sears Tower) at 1,451 feet. Since then, supertall buildings have multiplied worldwide, particularly in the Middle East and Asia. Among these are the Burj Khalifa in Dubai, completed nearly a decade after 9/11 and currently the tallest skyscraper at 2,717 feet, also designed by the Chicago-based firm Skidmore, Owings & Merrill (SOM).
Chicago itself has seen modest growth in supertall structures, increasing from five to seven with the addition of the Trump Tower and The St. Regis Chicago. However, the city has largely stepped back from the global competition to build the tallest towers, a race now dominated by cities in the Middle East and East Asia. For example, the proposed Kingdom Tower in Jeddah, Saudi Arabia, designed by Adrian Smith + Gordon Gill Architecture, is planned to reach 3,281 feet, potentially surpassing the Burj Khalifa.
Security concerns following 9/11 have also influenced architectural design and urban planning. The 48-story 71 South Wacker building, completed in 2005, was the first major commercial tower in Chicago designed post-9/11. Developers abandoned earlier, more ambitious designs, opting instead for a project featuring subtle security measures, such as large planters to prevent vehicular attacks and integrated screening procedures. Similarly, federal buildings in Chicago’s Federal Center underwent significant security alterations. The installation of granite bollards along streets has disrupted the original open design conceived by architect Ludwig Mies van der Rohe, which aimed to reflect transparency and democratic ideals.
While the Twin Towers symbolized American economic power to the 9/11 attackers, the towers themselves had been surpassed in height by other structures decades prior, ranking fifth and sixth globally by 2001. In the years since, both Chicago and New York City, the sites of those attacks, have focused more on sustainable and qualitative urban development rather than height alone.
Today’s skyscrapers incorporate enhanced safety features, such as reinforced stairwells and improved fire resistance, though these advancements are often unseen. The evolution of skyline design since 9/11 exemplifies a balance between architectural ambition, urban security, and symbolically resonant construction. As the cities adapt, their distinctive skylines persist without necessarily seeking new height records, reflecting changing priorities in a complex post-9/11 world.