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 crowns of kings and nobles, the emerald, the topaz, the ruby, the diamond, all came from the East--mainly from India.

The whole of mediaeval medical science was derived from the Arabs, who sought most of their drugs from Arabia or India.