early in the fifteenth
century, encountered dangers and difficulties unknown to Marco Polo a
hundred years earlier. The successors of Kublai Khan no longer ruled in
China; while the Ilkhans of Persia, having long since adopted
Mohammedanism, were now as ill-disposed as formerly they had been
friendly toward Christian states. Eastern and central Asia was indeed
once more closing to Europeans: its rulers no longer sought alliance
with Christian princes; no longer requested the service of papal
missionaries; no longer welcomed traders and travelers. And in the
Levant itself ominous changes were portending: the Ottoman Turks,
pressing upon the Greek Empire from Asia Minor and the Balkan Peninsula,
were already well advanced upon their career of blighting conquest which
was destined to throw Christendom upon the defensive for more than two
centuries. At the opening of the fifteenth century, although the trade
routes had not been closed by the Turks, the _Drang nach Osten_--the
hope of cutting through the Moslem barrier in order to establish direct
connection with India--was at an end. Unless a new way to the East could
be found, the better part of the treasure of the Orient was lost to
Europe.

IV

Long before the fifteenth century many men had thought it possible to
reach India by sailing around Africa. Since classical times geographers
had both asserted and denied the possibility. During the Middle Ages the
Ptolemaic theory was in the ascendant; but the observations of
thirteenth-century travelers gave powerful support to the ideas of
Eratosthenes. Europeans who had sailed from Malacca to Hormos, or had
read the book of Marco Polo or Friar Oderic, knew well that no
impenetrable swamp guarded the southern approaches to Asia; while those
who had seen or heard of Arab ships clearing from Calicut for Aden could
scarcely avoid the inference that a wider sweep to the south might have
brought the same ships to Lisbon or Venice.

This inference, the alert and practical Italian intellect, unhampered
by scientific tradition or ecclesiastical prejudice, had unhesitatingly
drawn. The famous Laurentian _Portolano_, a sailing chart constructed in
1351, was precisely such a map as Marco Polo, had he turned
cartographer, might have drawn: the first map in which Africa appears
familiar to modern eyes; with the point of the continent foreshortened,
and the Atlantic and Indian Oceans joined at last, it held out to all
future explorers