The Old Post Office, listed on the National Register of Historic Places as the Old Post Office and Clock Tower, is located at 1100 Pennsylvania Avenue, N.W. in Washington, D.C. It is a contributing property to the Pennsylvania Avenue National Historic Site. Construction began in 1892 and was completed in 1899. The building is an example of Richardsonian Romanesque, part of the Romanesque Revival architecture of the 19th-century United States.