Modern Heidelberg can trace its beginnings to the fifth century. The village Bergheim (Mountain Home) is first mentioned in that period, in documents dated to 769 AD. Bergheim now lies in the middle of modern Heidelberg. The people gradually converted to Christianity. In 863 AD, the monastery of St. Michael was founded on the Heiligenberg inside the double rampart of the Celtic fortress. Around 1130, the Neuberg Monastery was founded in the Neckar valley. At the same time, the bishopric of Worms extended its influence into the valley, founding Schönau Abbey in 1142. Modern Heidelberg can trace its roots to this 12th-century monastery. The first reference to Heidelberg can be found in a document in Schönau Abbey dated to 1196. This is considered the founding date for Heidelberg. In 1155, Heidelberg castle and its neighboring settlement were taken over by the house of Hohenstaufen. Conrad of Hohenstaufen became Count Palatine of the Rhine (German: Pfalzgraf bei Rhein). In 1195, the Electorate of the Palatinate passed to the House of Welf through marriage.