The Koster Site, south of Eldred, Illinois, preserves an unusually deep and continuous record of human occupation in the Illinois River valley. Discovered in 1967 and extensively excavated from 1969 to 1978, it revealed 25 distinct occupations spanning from about 7500 BC to about AD 1000. This long sequence let archaeologists trace repeated settlement in one place over thousands of years. Evidence of permanent residences, stone tools, food-grinding, and dog burials challenged assumptions about purely nomadic early life in North America. The site also contains one of the oldest known cemetery areas in eastern North America and became a landmark in American archaeology.