Sand dunes are accumulations of windblown sand piled up in mounds or ridges. Located nearby are several ancient burial mounds (kurgans) and excavated cities. The round halves of these burial mounds contain burial chambers. Dunes are structures formed by wind moving sediments into mounds. The Adena began constructing large earthwork mounds around 600 BCE. They buried their dead in long low burial mounds. Illinois researchers discovered the remains of several earthwork mounds. Each has platforms, pyramidal mounds, residential areas and tombs. Many Coles Creek sites were erected over earlier Woodland period mortuary mounds. Their presence is still seen in the preserved burial mounds. In about this time the largest royal burial mounds were erected. A past buried under mounds of earth and ignorance. Lagash is one of the largest archaeological mounds in the region, measuring roughly . There have been five Bronze Age burial mounds, or cairns, recorded on Friars Point. Numerous mounds and settlements from Iron Age were discovered there.