The whole country has been occupied by the French troops of the Sudan, and some rather scanty data may be found in the Renseignements coloniaux published by the Comite de l’Afrique Francaise. Even more important material on this region has been furnished by the Tilho expedition of 1912–17, which made a long study of it, and the Tilho map particularly gives us a perfectly clear image of the Tibbu Sahara. The Tibesti belongs decisively to the Saharan domain. The Tibesti have one great stronghold which has remained impregnable throughout all the ages. This is the Tibbus, a counterpart, a twin of the Ahaggar. There are certain other oases which as regards their inhabitants should be considered Tibbu territory. Among these are Gatron in southern Fezzan, and Kawar, which lies west of the Tibesti and includes the salt mines of Bilma.