Noted for its striking position atop a plateau of friable volcanic tuff overlooking the Tiber river valley, Civita di Bagnoregio was founded by Etruscans more than 2500 years ago. In constant danger of destruction as the edges of the plateau collapse due to erosion and earthquakes, Civita started its decline by the 16th century, and it is now known as "La città che muore" ("The Dying Town"). The population today varies from about 7 people in the Winter to more than 100 in the Summer. The town is on the World Monuments Fund's 2006 Watch List of the 100 Most Endangered Sites, because of threats it faces from erosion and unregulated tourism.