[Sidenote:  Depredation and conquests of African nomads.]

All the Saharan tribes are marauders, whether Arabs, Berber Tuaregs, or Negroid Tibbus.  The desert has made them so.  The Tuaregs are chronic freebooters; they keep the Sahara and especially the caravan routes in constant insecurity.  They stretch a cordon across these routes from Ghadames and Ghat in the east to the great oases of Insalah and Twat in the west; and from the oases and hills forming their headquarters they spread for pasturage and blackmail over the desert.[1078] They exact toll over and over again from a caravan, provide it with a military escort of their own tribesmen, and then pillage it on the way.[1079] This has been the experience of Barth[1080] and other explorers.  Caravans have not been their only prey.  The agricultural peoples in the Niger flood-plain, the commerce on the river, and the markets of Timbuctoo long suffered from the raids of the Tuaregs of the Sahara.  They collected tribute in the form of grain, salt, garments, horses and gold, typical needs of a desert people, imposed tolls on caravans and on merchant fleets passing down the Niger to Timbuctoo.  In 1770 they began to move from the desert and appropriate the fertile plains in the northern part of the Niger Valley, and in 1800 they conquered Timbuctoo; but soon they had to yield to another tribe of pastoral nomads, the Fulbes from the Senegal, who in 1813 established a short-lived but well organized empire on the ruins of the Tuareg dominion.[1081] [See map page 105.] The other agricultural states of the Sudan have had the same experience.  The Tibbus, predatory nomads of the French Sahara just north of Lake Chad and the River Yo, mounted on camels and ponies, cross the shrunken river in the dry season and raid Bornu for cattle, carry off women and children to sell as slaves, pillage the weekly markets on the Yo, and plunder caravans of pilgrims moving eastward to Mecca.[1082] Nowhere can desert nomads and the civilized peoples of agricultural plains dwell side by side in peace.  Raids, encroachments, reprisals, finally conquest from one side or the other is the formula for their history. [See map page 487.]

[Sidenote:  Forms of defense against nomad depredations.]

The raided territory, if a modern civilized state, organizes its border communities into a native mounted police, as the English have done in Bornu, Sokoto and the Egyptian Sudan, and as the Russians did with their Cossack riders along the successive frontiers of Muscovite advance into the steppes; or it takes into its employ, as we have seen, the nearest nomad tribes to repress or punish every hostile movement beyond.  Among the ancient states the method was generally different.  Since the nomad invaders came with their flocks and herds, a barrier often sufficed to block their progress.  For this purpose Sesostris built the long wall of 1500 stadia from Pelusium to Heliopolis as a barricade against the Arabians.[1083]