region in northern Chad, centred around the town of Faya (formerly Largeau). It is mostly a sandy desert of the southeastern Sahara, south of the Tibesti massif and west of the Ennedi plateau. Formerly a vassal state of Ouaddaï, a Muslim (Sanūsī) sultanate, it was ceded to France under an Anglo-French agreement (1899), but Sanūsī control over the region was not broken until 1913–14. French troops remained in Borkou (and neighbouring Ennedi and Tibesti) until 1965 because the area was considered hard to control. The more fertile oases grow dates, barley, and vegetables and support camels, donkeys, and goats. The area is drained underground by the Lake Chad Basin. The population consists of nomadic and semi-nomadic Tedas, Arabs, and Berbers.