In Modern architecture we have operated too long under the restrictions of unbending rectangular forms supposed to have grown out of the technical requirements of the frame and the mass-produced curtain wall. In contrasting Mies' and Johnson's Seagram Building (74) with Kahn's project for an office tower in Philadelphia (75) it can be seen that Mies and Johnson reject all contradictions of diagonal wind-bracing in favor of an expression of a rectilinear frame. Kahn once said that the Seagram Building was like a beautiful lady with hidden corsets. Kahn, in contrast, expresses the wind-bracing-but at the expense of such vertical elements as the elevator and, indeed of the spaces for people.