The section of downtown Pittsburgh around Mellon Square includes the foremost concentration of prominent commercial and institutional buildings from the late nineteenth and early twentieth centuries in Pittsburgh's central business district. Laid out as part of the original plan of Pittsburgh in 1784, the Mellon Square area was largely residential for about a century. However, the changes that took place in the city in the late nineteenth century - the great urban growth and industrial concentration - transformed Pittsburgh into an industrial power and its downtown into a central business district. The buildings in this area represent that stage of the city's history, showing the influence of Pittsburgh's industrialists and corporations and the creativity of some of the best architects in the United States at the turn of the century.
Remnants of the original nineteenth-century residential character of the center of downtown Pittsburgh can be found in the Mellon Square area. Eight churches stood in this section in 1900; three of the four that survive near Mellon Square received land grants for their sites from the sons of William Penn in 1787. On one of these sites remains the oldest use in the area - the church graveyard of Trinity Cathedral on Sixth Avenue. There is also a small fragment of this residential character in the small (former) houses along Strawberry Way at Montour Way.
The Mellon Square area is dominated by the buildings that were built in the area at the turn of the century to house and serve the major industrial corporations and their ranks of white-collar employees. All of the principal institutions that developed in Victorian society could be found there, including clubs (especially the Duquesne Club), banks (principally the Mellon Bank), department stores, office buildings, and even downtown churches (as the old churches were rebuilt on their old sites). The office buildings at the turn of the century were representative of the great industrialists - Park, Carnegie, Frick, Oliver. Later, though, in the Twenties, as industry became dominated by faceless corporations, so the new office buildings became memorials to those companies (Koppers, Gulf, Alcoa).
The developers of the significant buildings around Mellon Square turned to the best of local and national architects to design those buildings. Among the nationally-known architects who came to Pittsburgh were George Post (the Park Building), Trowbridge and Livingston (Mellon Bank and the Gulf Building), and Harrison and Abramovitz (the Regional Enterprise Tower) of New York and Daniel H. Burnham of Chicago (the Frick Building, McCreery Department Store, and Oliver Building). Significant local architects who contributed their skills to this district included Henry Hornbostel (Smithfield Church), Charles Bickel (Granite Building), Frederick Osterling (the Union Trust Building), and Benno Janssen (Kaufmann's Department Store and the William Penn Hotel).
After World War Two, public and private interests in Pittsburgh combined in an effort to revitalize the Downtown area, called the "Pittsburgh Renaissance". While much of this effort took place outside of the Mellon Square area, Mellon Square itself was one of the cornerstone projects of the Renaissance effort. The Square, which is an underground parking garage with a public plaza on top, was carved out of the middle of the Golden Triangle to provide much-needed open space in a densely-built section of the city. Together with the Regional Enterprise Tower next door, Mellon Square marks a high point in planning and design in the redevelopment programs of the 1950s.
In 1985, the value of the entire Mellon Square section of Downtown Pittsburgh was recognized when the Pittsburgh Downtown Historic District was listed in the National Register of Historic Places.