world's trade routes and of geographical tradition, science and
seamanship were so little advanced. Between Ptolemy and Henry of
Portugal, between the second and the fifteenth centuries, the only great
extension of men's knowledge of the world was: (1) in the extreme north,
where the semi-Christian, semi-Pagan Vikings reached perhaps as far as
the present site of New York and founded, on another side, the Mediæval
Kingdom of Russia; (2) on the south-east coast of Africa, from Cape
Guardafui to Madagascar, which was opened up by the trading interest of
the Emosaid family (800-1300); (3) in the far east, in Central and
Further Asia, by the discoveries of Marco Polo and the Friar preachers
following on the tracks of the earlier Moslem travellers. The first of
these was a Northern secret, soon forgotten, or an abortive development,
cut short by the Tartars; the second was an Arabic secret, jealously
guarded as a commercial right; the third alone added much direct new
knowledge to the main part of the civilised world.

But throughout their period of commercial rule from the eighth to the
twelfth centuries, the Arabs took a keen interest in land traffic,
conquest, and exploration. They were of small account at sea; it took
them some time to turn to their own purposes Hippalus' discovery (in the
second century A.D.) of the monsoon in the Indian Ocean; but, on land,
Moslem travellers and writers--generally following in the wake of their
armies, but sometimes pressing on ahead of them--did not a little to
enlarge the horizon of the Mohammedan world, though it was not till
Marco Polo and the Franciscan missionaries of the thirteenth and
fourteenth centuries, that Christian Europe shared in this gain.

As the early Caliphs conquered, they made surveys of their new
dominions. Thus after Tarik and Mousa had overrun Spain, Walid at
Damascus required from them an account of the land and its resources.