evidence: Cameroon,[a] officially the Republic of Cameroon,[b] is a country in Central Africa. It shares boundaries with Nigeria to the west and north, Chad to the northeast, the Central African Republic to the east, and Equatorial Guinea, Gabon, and the Republic of the Congo to the south. Its coastline lies on the Bight of Biafra, part of the Gulf of Guinea, and the Atlantic Ocean. Due to its strategic position at the crossroads between West Africa and Central Africa, it has been categorized as being in both camps. Cameroon's population of nearly 31 million people speak 250 native languages, in addition to the national tongues of English and French, or both. Early inhabitants of the territory included the Sao civilisation around Lake Chad and the Baka hunter-gatherers in the southeastern rainforest. Portuguese explorers reached the coast in the 15th century and named the area Rio dos Camarões (Shrimp River), which became Cameroon in English. Fulani soldiers founded the Adamawa Emirate in the north in the 19th century, and various ethnic groups of the west and northwest established powerful chiefdoms and fondoms. [...] Cameroon has four patterns of drainage. In the south, the principal rivers are the Ntem, Nyong, Sanaga, and Wouri. These flow southwestward or westward directly into the Gulf of Guinea. The Dja and Kadéï drain southeastward into the Congo River. In northern Cameroon, the Bénoué River runs north and west and empties into the Niger. The Logone flows northward into Lake Chad, which Cameroon shares with three neighbouring countries.[99]