Mellon Square is an urban park in Downtown Pittsburgh, Pennsylvania. It is the first Modernist park built above a parking garage. With its distinctive black-and-white geometric pavement, it is a prominent feature and gathering spot of Downtown Pittsburgh. The square, bounded by Smithfield Street, William Penn Place, and Oliver and Sixth avenues, is surrounded by many prominent downtown buildings including the Oliver Building, 525 William Penn Place, Omni William Penn Hotel, and the Regional Enterprise Tower. It has long been a popular lunchtime destination for downtown workers.
In addition, retail shops are housed underneath it, along the Smithfield Street side of the square. After World War II, the Aluminum Company of America (ALCOA), which was established in Pittsburgh in the 19th century, proposed to move to New York City. Banker Richard King Mellon aimed to block the move. In 1949 he proposed a new downtown headquarters building for ALCOA (now the Regional Enterprise Tower).