Chad (Arabic: تشاد (Tšad); French: Tchad), officially the Republic of Chad, is a landlocked country in central Africa. It is listed by Foreign Policy as one of the world's top 10 failed states. It borders Libya to the north, Sudan to the east, the Central African Republic to the south, Cameroon and Nigeria to the southwest, and Niger to the west. Due to its distance from the sea and its largely desert climate, the country is sometimes referred to as the "dead heart of Africa". In the north, it contains the Tibesti Mountains, the largest mountain chain in the Sahara desert. Chad was formerly part of the Federation of French Equatorial Africa.
Chad's terrain is dominated by the low-lying Chad Basin (elevation about 250 m / 820 ft), which rises gradually to mountains and plateaus on the north, east, and south. In the east heights of more than 900 metres (3,000 ft) are attained in the Ennedi and Ouaddaï plateaus. The greatest elevations are reached in the Tibesti massif in the north, with a maximum height of 3,415 metres (11,204 ft) at Emi Koussi. The northern half of the republic lies in the Sahara. The only important rivers, the Logone and Chari (Shari), are located in the southwest and flow into Lake Chad. The lake doubles in size during the rainy season