The Sao civilization (also called So) flourished in Central Africa from ca. the fourth or sixth century BC to as late as the sixteenth century AD. The Sao lived by the Chari River basin in territory that later became part of Cameroon and Chad. They are the earliest civilization to have left clear traces of their presence in the territory of modern Cameroon. Sometime around the 16th century, conversion to Islam changed the cultural identity of the former Sao. Today, several ethnic groups of northern Cameroon and southern Chad, but particularly the Sara, Kotoko, claim descent from the civilization of the Sao.