From the Neolithic onwards the chalk downland of the area that would become Wessex was traversed by the Harrow Way, which can still be traced from Marazion in Cornwall to the coast of the English Channel near Dover, and was probably connected with the ancient tin trade. In the Late Neolithic, the ceremonial sites of Avebury and Stonehenge were completed on Salisbury Plain, but the final phase of Stonehenge was erected by the so-called Wessex culture of the Middle Bronze Age (c. 1600-1200 BC). The area has many other earthworks and erected stone monuments from the Neolithic and Early Bronze periods, including the Dorset Cursus, an earthwork long and wide, which was oriented to the midwinter sunset. Although agriculture and hunting were pursued during this long period, there is little archaeological evidence of human settlements. By the Iron Age, Celtic British tribes such as the Durotriges, Atrebates, Belgae and Dobunni occupied the future Wessex.