Between 500 B.C. and A.D. 150, an ancient culture built an extensive complex of burial mounds and earthworks throughout the Kanawha River Valley. Probably built in the Woodland period after 500 B.C., the Kanawha Valley mounds were used as burial sites for hundreds of years, as suggested by recovered artifacts. The complex, called "Ancient Kanawha City" by Smithsonian archaeologist Cyrus Thomas, extended from Charleston to Dunbar and included more than 50 earthen mounds, extensive earthen enclosures, hollow stone heaps, and numerous graded roadways connecting the mounds, all situated on upper terraces of the Kanawha River. The mounds ranged from 35 to 200 feet in diameter and from 3 to 35 feet in height. The valley once had the largest concentration of Adena burial mounds in the Ohio River basin, and hollow stone heaps were built along cliffs overlooking the Kanawha River from Huntington to above Montgomery. Building the South Charleston Mound required people to hand-carry more than a million individual baskets of dirt, and its tombs indicate a society with a social hierarchy that honored its dead and may have used the mound for burials over hundreds of years. After years of land development, only a few mounds remain, and no earthworks or stone heaps are known to survive.