were, a skeleton of the geographical knowledge summed
up in the great work of Ptolemy.

But of more importance for the future development of geographical
knowledge were the great caravan routes of Asia, to which we must
now turn our attention. Asia is the continent of plateaux which
culminate in the Steppes of the Pamirs, appropriately called by
their inhabitants "the Roof of the World." To the east of these,
four great mountain ranges run, roughly, along the parallels of
latitude--the Himalayas to the south, the Kuen-Iun, Thian Shan,
and Altai to the north. Between the Himalayas and the Kuen-lun is
the great Plateau of Tibet, which runs into a sort of cul-de-sac
at its western end in Kashmir. Between the Kuen-lun and the Thian
Shan we have the Gobi Steppe of Mongolia, running west of Kashgar
and Yarkand; while between the Thian Shan and the Altai we have
the great Kirghiz Steppe. It is clear that only two routes are
possible between Eastern and Western Asia: that between the Kuen-lun
and the Thian Shan via Kashgar and Bokhara, and that south of the
Altai, skirting the north of the great lakes Balkash, Aral, and
Caspian, to the south of Russia. The former would lead to Bassorah
or Ormuz, and thence by sea, or overland, round Arabia to Alexandria;
the latter and longer route would reach Europe via Constantinople.
Communication between Southern Asia and Europe would mainly be
by sea, along the coast of the Indies, taking advantage of the
monsoons from Ceylon to Aden, and then by the Red Sea. Alexandria,
Bassorah, and Ormuz would thus naturally be the chief centres of
Eastern trade, while communication with the Mongols or with China
would go along the two routes above mentioned, which appear to have
existed during all historic time. It was by these latter routes
that the Polos and the other mediaeval travellers to Cathay reached
that far-distant country. But, as we know from Marco Polo's travels,
China could also be reached by the sea voyage; and for all practical
purposes, in the late Middle Ages, when the Mongol empire broke
up, and traffic through mid Asia was not secure, communication
with the East was via Alexandria.

Now it is important for our present inquiry to realise how largely
Europe after the Crusades was dependent on the East for most of the
luxuries of life. Nothing produced by the looms of Europe could
equal the silk of China, the calico of India, the muslin of Mussul.
The chief gems which decorated the