Most of Chad is large basin bordered by mountains and highlands in the north, east, and south. A vast Inland Sea once filled the depression, of which Lake Chad is remnant. Neolithic rock paintings exist in the northern mountains, and the archaeological evidence around the lake and its two main tributaries, the Logone and Shari rivers, suggests the existence of a settled civilization as early as the 9th century. Chad has three climatic zones. The north is arid, and vegetation is limited to scattered oases, the south is tropical, with flora characterized by light woodlands and grasslands. In the semiarid middle region, at the latitude of N'diamena, the drier grasslands give way to thronbush. The rainy season lasts from May to October and is somewhat longer in the south, with annual precipitation increasing form 300 to 1,270mm or 12 to 50 inches, between the capital and the far south. In the northern Saharan region, rainfall is rare, with less than 25mm or 1 inch annually. Temperatures range from 27 degrees Celsius to around 30 degrees Celsius or 80 to 100 degrees Fahrenheit. Animal life is varied, and Lake Chad and the Shari and Logone rivers are among the richest sources of fish in Africa.
The many different ethnic groups in Chad include the Sara peoples in the south, the Eulani, Barma, Kanembu, Arabs, and the Maba in the middle zone, the nomadic Teda, Daza, and Tubu in the north, and the Kotoko along the rivers. Most