Pennsylvania Avenue National Historic Site: The Pennsylvania Avenue National Historic Site comprises a large portion of the federal and local governmental cores.
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Contained within the irregular bounds of the Pennsylvania Avenue National Historic Site is a rich selection of building types and styles, statues, memorials, and parks. Additionally, the area features many prominent elements that date from Pierre Charles L'Enfant's 1891 plan for the City of Washington, as amplified in 1901-02 by the McMillan Commission.
The National Historic Site provides the urban setting for such naturally recognized features as the Treasury Building, the buildings of Federal Triangle, Ford's Theater, the Old Patent Office, and the buildings centered around Judiciary Square. It is also home to many lesser-known but historically significant residential and commercial buildings, statues, and memorials, as well as numerous parks and landscape features. It includes approximately 160 contributing buildings that date from about 1791 to 1930.
DC Inventory: June 19, 1973 (Joint Committee on Landmarks)
National Register and National Historic Site: October 15, 1966 (amended October 12, 2007)
Files

Aerial view of Pennsylvania Avenue Federal Triangle, Washington, D.C., 2006
Highsmith, Carol M, photographer. Aerial view of Pennsylvania Avenue Federal Triangle, Washington, D.C. 2006. Image. Retrieved from the Library of Congress, https://www.loc.gov/item/2010630811/. (Accessed September 12, 2016.)
Seventh Street, Washington, D.C., under the flood, 1889

Pennsylvania Avenue National Historic Site, circa 1846

Whitlows, Pennsylvania Avenue National Historic Site

Hardy, Pennsylvania Avenue National Historic Site

Old Post Office Building located on Pennsylvania Avenue in Washington, D.C., 2012
Highsmith, Carol M, photographer. Old Post Office Building located on Pennsylvania Avenue in Washington, D.C. January, 2012. Image. Retrieved from the Library of Congress, https://www.loc.gov/item/2013634610/. (Accessed September 12, 2016.)