The impulse for the enslavement of negroes by other peoples came from the Arabs who spread over northern Africa in the eighth century, conquering and converting as they went, and stimulating the trade across the Sahara until it attained large dimensions.  The northbound caravans carried the peculiar variety of pepper called “grains of paradise” from the region later known as Liberia, gold from the Dahomey district, palm oil from the lower Niger, and ivory and slaves from far and wide.  A small quantity of these various goods was distributed in southern Europe and the Levant.  And in the same general period Arab dhows began to take slave cargoes from the east coast of Africa as far south as Mozambique, for distribution in Arabia, Persia and western India.  On these northern and eastern flanks of Guinea where the Mohammedans operated and where the most vigorous of the African peoples dwelt, the natives lent ready assistance in catching and buying slaves in the interior and driving them in coffles to within reach of the Moorish and Arab traders.  Their activities, reaching at length the very center of the continent, constituted without doubt the most cruel of all branches of the slave-trade.  The routes across the burning Sahara sands in particular came to be strewn with negro skeletons.[5]

[Footnote 5:  Jerome Dowd, “The African Slave Trade,” in the Journal of Negro History, II (1917), 1-20.]

This overland trade was as costly as it was tedious.  Dealers in Timbuctoo and other centers of supply must be paid their price; camels must be procured, many of which died on the journey; guards must be hired to prevent escapes in the early marches and to repel predatory Bedouins in the later ones; food supplies must be bought; and allowance must be made for heavy mortality among the slaves on their terrible trudge over the burning sands and the chilling mountains.  But wherever Mohammedanism prevailed, which gave particular sanction to slavery as well as to polygamy, the virtues of the negroes as laborers and as eunuch harem guards were so highly esteemed that the trade was maintained on a heavy scale almost if not quite to the present day.  The demand of the Turks in the Levant and the Moors in Spain was met by exportations from the various Barbary ports.  Part of this Mediterranean trade was conducted in Turkish and Moorish vessels, and part of it in the ships of the Italian cities and Marseilles and Barcelona.  Venice for example had treaties with certain Saracen rulers at the beginning of the fourteenth century authorizing her merchants not only to frequent the African ports, but to go in caravans to interior points and stay at will.  The principal commodities procured were ivory, gold, honey and negro slaves.[6]

[Footnote 6:  The leading authority upon slavery and the slave-trade in the Mediterranean countries of Europe is J.A.  Saco, Historia de la Esclavitud desde los Tiempas mas remotas hasta nuestros Dias (Barcelona, 1877), vol.  III.]