This primary source comes from the Records of the Office of the Chief of Engineers.
Full Citation: The Seat of War: Birds Eye View of Virginia, Maryland, Delaware, and the District of Columbia; 1861; Drawer 150; Fortifications Map File Plans of Military Forts, 1818 - 1941; Records of the Office of the Chief of Engineers, Record Group 77; National Archives at College Park, College Park, MD. [Online Version, https://docsteach.org/documents/document/birds-eye-view-virginia-maryland-delaware-dc, May 14, 2024]