York, 1914).]

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