There is evidence of early Daza settlements in the Tibesti; however, these early clans—the Goga, Kida, Terbouna and Obokina—were assimilated into later Daza clans, who arrived in the Tibesti between the 15th and 18th centuries, having fled the Kanem-Bornu Empire in the southwest after the Toubou allied with a Kanem enemy, the Bilala. These later Daza arrivals include the Arna Souinga in the south, Gouboda in the center-west, Tchioda and Dirsina in the west, Torama in the northwest and center-east, and the Derdekichia (literally, descendants of the chief, the products of a union between an Arna Souinga and an Emmeouia) in the north. The Tibesti then played the role of an impregnable mountain stronghold for the newcomers. Meanwhile, constant migration between the north and southwest of Chad, along with significant mixing of the populations, forged a significant degree of cohesion among the Toubou ethnicities. Periods of territorial expansion in the 10th and 13th centuries and periods of recession in the 15th and 16th centuries likely coincided with more or less pronounced wet and dry periods.