Leslie Robertson, the principal engineer behind the World Trade Center, died Thursday. He was 92. Robertson had been diagnosed with blood cancer a year ago, and he died in his home in San Mateo, California. At the time of their construction, the World Trade Center towers were the tallest buildings in the world at 110 stories. Robertson also designed the structural systems for the Shanghai World Financial Center, the Bank of China Tower in Hong Kong, and several of the artist Richard Serra’s installations. In the aftermath of the 9/11 attacks, Robertson’s work on the World Trade Centers came under intense scrutiny, and he said he had never considered the possibility of a plane crash incinerating the building. He told The New York Times, “I have to ask myself, Should I have made the project more stalwart? And in retrospect, the only answer you can come up with is, yes, you should have.”