Due to Post-glacial rebound the islands in the Archipelago Sea suitable for habitation have risen from the sea and inhabitants have moved farther out in the archipelago as large enough islands have surfaced. The ground still rises in the Archipelago Sea at a rate of approximately 3-4,2 mm per year. During the Stone Age and the Bronze Age, the islets of the present-day outer archipelago were 20–25 metres below the sea level. Then outer archipelago was located around the present main islands of Nagu, Korpo and Houtskär. Nowadays, the Stone Age settlement of Bötesberget in the municipality of Dragsfjärd, from 6000 BCE, is located 55 metres above the sea level, on forested upland. In the old days, the landscape surrounding its inhabitants was quite different from today: the settlement was situated on an isolated island in the middle of large open water areas.