In exchange for the manifold products of the East, Europe had only rough woolen cloth, arsenic, antimony, quicksilver, tin, copper, lead, and coral to give; and a balance, therefore, always existed for the European merchant to pay in gold and silver, with the result that gold and silver coins grew scarce in the West. It is hard to say what would have happened had not a new supply of the precious metals been discovered in America. But we are anticipating our story. [Sidenote: Oriental Trade-Routes] Nature has rendered intercourse between Europe and Asia exceedingly difficult by reason of a vast stretch of almost impassable waste, extending from the bleak plains on either side of the Ural hills down across the steppes of Turkestan and the desert of Arabia to the great sandy Sahara. Through the few gaps in this desert barrier have led from early times the avenues of trade. In the fifteenth century three main trade-routes--a central, a southern, and a northern--precariously linked the two continents. (1) The central trade-route utilized the valley of the Tigris River. Goods from China, from the Spice Islands, and from India were brought by odd native craft from point to point along the coast to Ormuz, an important city at the mouth of the Persian Gulf, thence to the mouth of the Tigris, and up the valley to Bagdad. From Bagdad caravans journeyed either to Aleppo and Antioch on the northeastern corner of the Mediterranean, or across the desert to Damascus and the ports on the Syrian coast. Occasionally caravans detoured southward to Cairo and Alexandria in Egypt. Whether at Antioch, Jaffa, or Alexandria, the caravans met the masters of Venetian ships ready to carry the cargo to Europe. (2) The southern route was by the Red Sea. Arabs sailed their ships from India and the Far East across the Indian Ocean and into the Red Sea, whence they transferred their cargoes to caravans which completed the trip to Cairo and Alexandria. By taking advantage of monsoons,--the favorable winds which blew steadily in certain seasons,--the skipper of a merchant vessel could make the voyage from India to Egypt in somewhat less than three months. It was often possible to shorten the time by landing the cargoes at Ormuz and thence dispatching them by caravan across the desert of Arabia to Mecca, and so to the Red Sea, but caravan travel was sometimes slower and always more hazardous than sailing.