The country is largely a low-lying coastal plain and has many rivers, some with wide swampy estuaries. The chief towns are Gabú, Oio, Cacheu, and Bolama. About half of the inhabitants adhere to traditional beliefs, and 45% are Muslim; there is a small Christian minority. The population is comprised mainly of five ethnic groups: the Balante, the Fulani, the Mandjack, the Mandinka, and the Papel. Portuguese is the official language, but Crioulo (a Portuguese creole) and a number of African languages are also spoken.