Madagascar, the fourth-largest island in the world, lies in the Indian Ocean off Mozambique's coast and includes several much smaller islands. A central chain of high mountains, the Hauts Plateaux, occupies more than half the main island and is responsible for the marked ethnic, climatic, and scenic differences between the east and west coasts. The narrow strip of eastern lowlands, settled from the 6th century by Polynesian seafarers, is largely covered by dense rainforests, whereas the broader western landscape, once covered by dry deciduous forests, is now mostly savannah. The east coast receives the monsoon and, on both coasts, the climate is wetter towards the north. The southern tip of the island is semi-desert, with great forests of cactus-like plants. The capital, Antananarivo, is high up in the Hauts Plateaux near the island's center. Much of Madagascar's flora and fauna is unique to the island.