The General Post Office, also known as the Tariff Commission Building, is a historic building at 700 F Street NW in Washington, D.C., United States. Built in 1839 to a design by Robert Mills and enlarged in 1866 to a design by Thomas U. Walter, it is an example of Greek Revival architecture. It was designated a US National Historic Landmark in 1971 for its architecture. The building has housed the Hotel Monaco since 2002.