After both towers of the World Trade Center were hit on September 11, 2001, first responders coordinated the largest emergency response in New York City’s history. But their heroism at Ground Zero was hampered by institutional bureaucracy and ultimately undone by decisions made decades earlier, when the Twin Towers were built.

So why did these iconic structures and architectural marvels fall so fast? Could more people have been rescued from the towers? And could some of those deaths have been avoided?