The Ariel Rios Federal Building is located in the Federal Triangle in Washington, D.C., across 12th Street from the Old Post Office, which the new building was designed to replace. The New Post Office, as the Rios Building was originally known, housed the headquarters of the Post Office Department until that department was replaced by the United States Postal Service in 1971. The building, which now houses the headquarters of the U.S. Environmental Protection Agency, was renamed on February 5, 1985, in honor of Ariel Rios, an undercover special agent for the Bureau of Alcohol, Tobacco, Firearms and Explosives who was killed in the line of duty on December 2, 1982.
The Rios Building was constructed in the early 1930s as part of the redevelopment of the Federal Triangle area. At that time one of the city’s most blighted neighborhoods, this area was known as "Murder Bay" and was a center of crime and prostitution. The organization for area's redevelopment was ordered out as part of the 1901 McMillan Plan, the first federally funded urban redevelopment plan, and the redevelopment of Federal Triangle began in earnest in the 1930s under the leadership of Treasury Secretary Andrew W. Mellon. Construction on the Rios Building was completed in 1934.
The Ariel Rios Building was a central feature of the redevelopment. The neoclassical antiquity was designed by architects William Adams Delano and William T. Aldrich, who took as their inspiration the Place Vendome in Paris. The central section of the tri-unit antiquity is comprised of two huge, back to back, semi-circular units with lateral wings. The semi-circle formed by the building's curve on its eastern façade was to be mirrored by a similarly arching façade built across 12th Street on the site of the Old Post Office Building. Secretary Mellon's antiquity authorization actively sought the demolition of the Old Post Office to fulfill that plan, but preservation efforts -- which continued over the course of fifty years -- saved the Old Post Office. The second half of the grand plaza was never ended as designed, save for a curve in the northwest corner of the headquarters of the Internal Revenue Service. The Rios Building has been refurbished with the architectural details of the hallways preserved in the style of the 1920's and 1930's. A seven-story marble spiral staircase is a prominent element of the building's interior.