The John Hancock Center's external X-bracing — the structural system that allows a 100-story tower to resist wind loads without interior shear walls — becomes, at close range and from the right angle, pure abstraction: intersecting diagonals of steel repeating up the face of the building in a pattern that Greg titled "Torquere," the Latin for to twist. The structural engineers at Skidmore, Owings & Merrill in 1969 made the decision to leave the bracing exposed, to let the building's skeleton be its skin, and the result is one of the most photographed facades in Chicago for exactly that reason. The image holds the steel geometry from deep shadow to overcast sky, no detail lost — at a scale that rewards a large print. Architecture as argument.