Chad, officially the Republic of Chad, is a landlocked country located at the crossroads of North and Central Africa. It is bordered by Libya to the north, Sudan to the east, the Central African Republic to the south, Cameroon to the southwest, Nigeria to the southwest (at Lake Chad), and Niger to the west. Chad has a population of 16 million, of which 1.6 million live in the capital and largest city of N'Djamena. With a total area of around 1,300,000 km2 (500,000 sq mi), Chad is the fifth-largest country in Africa and the twentieth largest nation by area in the world. Chad has several regions: the Sahara desert in the north, an arid zone in the centre known as the Sahel and a more fertile Sudanian Savanna zone in the south. Lake Chad, after which the country is named, is the second-largest wetland in Africa. Chad's official languages are Arabic and French. It is home to over 200 different ethnic and linguistic groups. Islam (55.1 percent) and Christianity (41.1 percent) are the main religions practiced in Chad. There are more than 200 ethnic groups in Chad; with only basic attempts at unification, these groups continue to perceive themselves as largely autonomous in regards to the greater nation. The major cultural groups are divided primarily along geographic lines. The southern fifth of the country--which contains half of the nation's population--is primarily settled by the Sara people, who live sedentary lifestyles and are predominantly Christian. The northern region of the country is inhabited primarily by nomadic tribal groups, who are mostly Muslim. The center of the country--the Sahel region--is a blending of nomadic and sedentary peoples.