Having more than 1300 earthen buildings in the area, Nanjing county is reputed as the "Earthen Building Kingdom". Earthen buildings in Nanjing originated before the 11th century and many of the existing buildings has a history over 300 years. The existing tallest, largest, smallest, most unique, and best-preserved earthen buildings can all be found there. Four of them have been listed as World Cultural Heritage sites: Huaiyuan Building, Hegui Building, Tianluokeng Earthen Building Cluster, and Hekeng Earthen Building Cluster.