The Arctic is a bleak, windy and icy land where the temperature can go down to –45ºC in winter and even the sea freezes. The moss-covered rocky ground, called tundra, is frozen hard for most of the time. In winter it is dark day and night, while in summer, there are weeks of continuous daylight, as the sun never sets. The people, known as Inuit, settled there in around 3,000 BC. They developed a way of life that allowed them to survive in this hostile environment. The Inuit used the skins of seals and walruses, to make warm waterproof clothing and to cover the wooden frames of kayaks and umiaks, their fast boats. They used sled dogs to pull sledges across the ice and snow. In the summer they moved inland to fish and hunt caribou with spears. For the winter, Inuit built snow-block houses known as igloos.