Grave finds from Singen am Hohentwiel date to the beginning of the Early Bronze Age and shore settlements were repeatedly built during the Neolithic Period and the Bronze Age (up to 800 BC). During the following Iron Age the settlement history is interrupted. The settlement of the shore of Lake Constance during the Hallstatt period is attested by grave mounds, which today are usually found in forests where they have been protected from the destruction by agriculture. Since the late Hallstatt period, the peoples living on Lake Constance are referred to as the Celts. During the La Tène period from 450 BC, the population density decreases, as can be deduced partly due from the fact that no more grave mounds were built. For the first time, written reports on Lake Constance have survived. Thus, we learn that the Helvetians settled by the lake in the south, the Rhaetians in the area of the Alpine Rhine Valley and the Vindelici in the north-east. The most important places on the lake were Bregenz (Celtic "Brigantion") and today's Constance.