 During the September 11 attacks, the stairs served as an escape route for hundreds of evacuees from 5 World Trade Center, a 9-floor building adjacent to the 110-story towers.The staircase is now an important feature of the National September 11 Memorial & Museum.The preservation of the staircase became a matter of dispute since May 11, 2006, when it was listed as one of America's Most Endangered Places by the National Trust for Historic Preservation.