Construction The bidding date, originally December 20, 1961, was postponed to January 22, 1962, to clarify the details of the arch construction . In 1959, ground was broken , and in 1961, the foundation of the structure was laid . Construction of the arch itself began on February 12, 1963, as the first steel triangle on the south leg was eased into place. These steel triangles, which narrowed as they spiraled to the top, were raised into place by a group of cranes and derricks. The arch was assembled of 142-foot-long (3.7 m) prefabricated stainless steel sections. Once in place, each section had its double-walled skin filled with concrete, prestressed with 252 tension bars . In order to keep the partially completed legs steady, a scissors truss was placed between them at 530 feet (160 m), later removed as the derricks were taken down . The whole endeavor was expected to be completed by fall 1964, in observance of St. Louis' bicentennial . Contractor MacDonald Construction Co. arranged a 30-foot (9.1 m) tower for spectators and provided recorded accounts of the undertaking. In 1963, a million people went to observe the progress, and by 1964, local radio stations began to broadcast when large slabs of steel were to be raised into place . The project manager of MacDonald Construction Co., Stan Wolf, said that a 62-story building was easier to build than the arch: "In a building, everything is straight up, one thing on top of another. In this arch, everything is curved ."