According to the Lietuvos piliakalnių atlasas (English: Atlas of Piliakalniai in Lithuania), there were 826 piliakalniai in Lithuania. Some researchers present a total number of 840 known piliakalnis in 2007; the number is likely to increase as even more of them are discovered every year. Most piliakalniai are located near rivers and are endangered by erosion: many have partly collapsed as the flooded river has washed out the base of the hill.