Today marks what would have been Fazlur Rahman Khan’s, a structural engineer who helped design some of America’s most iconic skyscrapers, 88th birthday. Khan’s most important contribution to modern day skyscrapers is his “trussed tube” system. Through his firm, Skidmore, Owing & Merrill, Khan’s design was first used in the Hancock building and then again in the iconic Sears Tower (Willis Tower today). This new system made it cheaper, safer and easier to build tall structures, especially over 40 stories high. His work shaped the way our cities look today.