When it opened on August 1, 1928, the Detroit Zoological Park was unique and progressive in its design. The Detroit Zoological Society commissioned Boston landscape architect Arthur Shurtleff to draw plans for the park according to the practices of Hamburg, Germany, landscape designer Carl Hagenback [sic], who promoted zoo exhibits without bars. Rather than being caged, the animals roamed freely in outdoor habitats bounded by moats and "rocks" made of reinforced concrete. Carl's son Heinrich came to supervise and build the exhibits. The Detroit Zoological Park is listed in the National Register of Historic Places.