Madagascar, the fourth-largest island in the world, lies in the Indian Ocean off the coast of Mozambique. It includes several much smaller islands. A central chain of high mountains, the Hauts Plateaux, occupies more than half of the main island and is responsible for the marked differences – ethnically, climatically and scenically – between the east and west coasts. The narrow strip of lowlands on the east coast, settled from the sixth century by Polynesian seafarers, is largely covered by dense rainforests, whereas the broader west-coast landscape, once covered by dry deciduous forests, is now mostly savannah.