Architect: Trowbridge and Livingston, with E.P. Mellon This forty-four story former corporate headquarters of the Gulf Oil Company was the tallest building in Pittsburgh until 1970. The limestone-covered steel shaft is capped by a stepped pyramid that recalls the Mausoleum of Halicarnassus. Until the 1970s, these steps were illuminated with neon that flashed a weather report to the city. A successful New York firm, Trowbridge and Livingston also designed the Mellon Bank on Mellon Square (1924).