- Robert N. C. Nix Federal Building - Philadelphia PAThe monumental Moderne-style Robert N. C. Nix Federal Building, sometimes known as the William Penn Annex, was constructed under the auspices of the federal Public Works Administration (PWA) between 1937 and 1941. Its exterior features multiple examples of New Deal artwork. The building was listed on the National Register of Historic Places in 1990. However, according to Mary Manfredi, the building is not listed on the Philadelphia Register and "it is not legally protected from alterations or demolition."