|The original nomination for the Pittsburgh Central Downtown Historic District established significance under NRHP Criterion A for commerce with the major concentration of prominent commercial and institutional historic buildings in Pittsburgh's central business district and under NRHP Criterion C for architecture as a cohesive concentration of resources reflecting nineteenth and twentieth century architectural styles (Aurand 1985:2). The newly contributing buildings of the listed district and boundary increase area similarly reflect bank, government, hotel, retail, and office buildings of pivotal importance to Pittsburgh's historic development and current health. .. [The buildings] represent the work of important architects and possess significant architectural qualities (Aurand 1985:4). They demonstrate the same wide variety of scale, age, style, materials, and function of the listed district with architecturally distinguished works. The amended period of significance for the district ranges from 1850 to 1962. It is amended because the period of significance in the earlier nomination (1850 to 1935) necessarily excluded resources that are of central importance to the commerce and architecture of the district but that were not yet fifty years old in 1985. This omission was noted in the original nomination, and the significance of the Alcoa Building and Mellon Square, in particular, were discussed at length (Aurand 1985). The amendment of the period of significance again defers to the fifty year cutoff date recommended by the NRHP for resources whose significance continues beyond the historic period. It acknowledges the continued importance of the district as the commercial heart of the city beyond 1962 demonstrated by the scope, scale, and variety of commerce that distinguishes this area from other parts of Downtown Pittsburgh. The amended period of significance also acknowledges that the newly contributing resources meet the standards established in the earlier nomination for high quality architecture with a role as a showplace for Pittsburgh's corporations and commercial enterprises.