Architect: Frederick Osterling This Flemish-Gothic style building was built by Henry Frick as a shopping arcade, known as the Union Arcade, with 240 shops and galleries on four levels. Lively terra cotta dormers and ornaments decorate the steeply pitched mansard roof, above which rise two chapel-like mechanical towers. The interior is organized around a central rotunda capped by a stained-glass dome. This building was built on the site of Pittsburgh's nineteenth-century Catholic cathedral. The architect, Frederick Osterling, was one of Pittsburgh's premier architects, and also designed the Arrott Building (1901-02), and the County Mortuary (1901-03).