Some time before 1454 a Portuguese factory was established at one of the
Arguim islands, and this factory soon systematized the slave-trade.
Thither came all kinds of merchandize from Portugal, and gold and slaves
were taken back in return; the number of the latter sent home annually, at
the time of Ca da Mosto's visit in 1454, being between seven and eight
hundred.

The narrative of the Portuguese voyages along the African coast is, for
the most part, rather uninviting. It abounds with names, and dates, and
facts; but the names are often hard to pronounce, the dates have sometimes
an air of uncertainty about them, and the facts stand out in hard relief,
dry and unattractive. Could we recall, however, the voyagers themselves,
and listen to their story, we should find it animating enough. Each
enterprise, as we have it now, with its bare statistics, seems a meagre
affair; but it was far otherwise to the men who were concerned in it. Of
the motives[4] impelling men to engage in such expeditions, something has
already been said.

[Footnote 4: "They err who regard the conquistadores as led only by a
thirst for gold, or even exclusively by religious fanaticism. Dangers
always exalt the poetry of life, and moreover, the powerful age which we
here seek to depict in regard to its influence on the development of
cosmical ideas, gave to all enterprises, as well as to the impressions
of nature offered by distant voyages, the charm of novelty and surprise,
which begins to be wanting to our present more learned age in the many
regions of the earth which are now open to us."--Humboldt's Kosmos.
Sabines translation, 1848, vol. ii. p. 272]