The Heiligenberg offers a good view of the plain and the river valley and offers a defensive position. Archaeological investigations have taken place there several times since 1881, including in the 1920s and 1930s during the building of a guest house and the Nazi-era Thingstätte; finds of Neolithic linear pottery show it was inhabited as early as 5500-5100 BCE. Celts settled there beginning in the first half of the first millennium BCE and constructed a double-walled hill fort around the primary and secondary peak. (The water source for this Celtic settlement, known as the Bittersbrunnen, was restored in 1979/80.)