with whom he had worked before (and who, like Kahn, was born in Estonia). Kahn generally referred to the museum's roof form as a vault, but Komendant explained that it was actually a shell playing the role of a beam. More precisely, as professor Steven Fleming points out, the shells that form the gallery roofs are "post-tensioned curved concrete beams, spanning an incredible 100 feet" (30.5 m), which "happened to have been the maximum distance that concrete walls or vaults could be produced without requiring expansion control joints." Both terms, vault and shell, are used in professional literature describing the museum. True vaults, such as the Roman vaults that Kahn admired, will collapse if not supported along the entire lengths of each side. Not fully understanding the capabilities of modern concrete shells, Kahn initially planned to include many more support columns than were necessary for the gallery roofs. Komendant was able to use post-tensioned concrete that was only five inches thick to create gallery "vaults" that need support columns only at their four corners. The Geren firm, which had been asked to look for ways to keep costs low, objected that the cycloid vaults would be too expensive and urged a flat roof instead. Kahn, however, insisted on a vaulted roof, which would enable him to create galleries with a comforting, room-like atmosphere yet with minimal need for columns or other internal structures that would reduce the museum's flexibility. Eventually a deal was struck whereby Geren would be responsible for the foundation and basement while Komendant would be responsible for the upper floors and cycloid shells. Kahn placed one of these shells at the front of each of the three wings as a porch or portico to illustrate how the building was constructed. The effect was, in his words, "like a piece of sculpture outside the building." Thos. S. Byrne, Ltd. was the contractor for the project, with A. T. Seymour as project manager. Virgil Earp and L. G. Shaw, Byrne's project superintendents, designed forms with a cycloid shape that were made from hinged plywood and lined with an oily coating so they could be reused to pour concrete for multiple sections of the vaults, helping to ensure consistency. The long, straight channels at the bottoms of the shells were cast first so they could be used as platforms to support the workmen pouring concrete for the cycloid curves. After