Detail of the south (left) and east faces of the Schoenborn family memorial in section D-South at Prospect Hill Cemetery in Washington, D.C., in the United States in 2014. Prospect Hill Cemetery was added to the Register of Historic Places of the District of Columbia (a listing of historic sites maintained by the city) in 2005. August Schoenborn (1827-1902) was a German American architect who designed the 1851 iron dome for the United States Capitol. He also designed Prospect Hill's 1873 gatehouse, was built near what was then the main gate on Lincoln Road.