end of 2013, about half the cemetery had been mapped, revealing a potential 2,750 unmarked burial sites. Cemetery staff said many of these burials are probably recorded, but some may be new discoveries. Congressional Cemetery officials said they were one of only 12 cemeteries in the city still accepting burials, and the mapping project would allow it to identify unused space. The mapping project was to be completed in the spring of 2014, and the cemetery said it would use the results to release a mobile phone app which will allow users to search for and locate graves on their own. In August 2013 the cemetery began using goats to eat and clear the surrounding wooded area of poison ivy, English ivy, grass, and other plants. The 58 "eco-goats", which cost $4,000, are considered more ecologically friendly than mowers and pesticides and provide fertilizer as well. It was the first use of goats inside the beltway. The use of the goats drew widespread international attention and televised reports on BBC World News, Nat Geo, News Hour, NBC Nightly News, Tokyo TV, China CCTV, and Al-Jazeera. Monuments and structures The Congressional Cemetery is a National Historic Landmark Historic District with 9 contributing structures and 186 contributing objects built from 1817 to 1876. Later structures and objects are considered to be "non-contributing" even if they are significant in the cemetery's current appearance. Cenotaphs Of the 186 contributing objects, 168 are the nearly identical Congressional cenotaphs, believed to have been designed by the Architect of the Capitol Benjamin Latrobe. As used at the Congressional Cemetery, the term "cenotaph" includes not only monuments to those buried elsewhere, but also to the Latrobe monuments that mark the actual graves of representatives and senators. Some congressmen are buried under a cenotaph, some are buried without one in a different area of the cemetery, and for some the marker is a true cenotaph. James Gillespie (1747–1805) who was reinterred in 1892, has a separate grave and cenotaph. A cenotaph was erected for each congressman who died in office from 1833 to 1876. The first was for Rep. James Lent. After Congress appropriated funds and his monument was ordered, his family reinterred the body in New York. Congress erected the monument in 1839 anyway, establishing the tradition of erecting cenotaphs. The cenotaphs are constructed of Aquia sandstone, as are the White House and the Capitol, and were likewise