More Science See Inside Castles in the Air The attacks of 9/11 supposedly ended the age of the skyscraper. A decade on we're building more than ever By Mark Lamster IWAN BAAN On that cool blue morning 10 years ago when everything changed, Les Robertson was half a world away, hosting a dinner at a Hong Kong restaurant. The rattling of cell phones left on the table—“a detestable habit”—was the first indication that something had struck one of the Twin Towers. Robertson, the revered engineer responsible for their structural design, was at first unconcerned. “I just assumed that a helicopter had run into the Trade Center,” he said recently, speaking from his 47th-floor office, which looks out over Ground Zero. Such an event, unfortunate as it might have been, was well within the tolerances for which the towers were designed. A few minutes later, however, when those cell phones started buzzing once more with news of a second crash, he realized it was “quite another thing again” and excused himself to watch the unfolding events from a hotel room. This is only a preview. Get the rest of this article now! Select an option below: Buy Digital Issue Customer Sign In *You must have purchased this issue or have a qualifying subscription to access this content It has been identified that the institution you are trying to access this article from has institutional site license access to Scientific American on nature.com. Click here to access this article in its entirety through site license access. ADVERTISEMENT Scientific American is a trademark of Scientific American, Inc., used with permission © 2015 Scientific American, a Division of Nature America, Inc. All Rights Reserved.