arth[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] Ancient Carthage constructed a ditch to check the
depredations of the nomads of Numidia.[1084] The early kings of Assyria
built a barrier across the plains of the Euphrates above Babylon to
secure their dominion f