The failed invasions of Japan and Java taught the Mongols much about shipbuilding, and when their military efforts failed, they turned that knowledge to peaceful pursuits of commerce. Khubilai Khan made the strategic decision to transport food within his empire primarily by ship because he realized how much cheaper and more efficient water transportation, which was dependent on wind and current, was than the much slower land transport, which was dependent on the labor of humans and animals that required constant feeding. In the first years, the Mongols moved some 3,000 tons by ship, but by 1329 it had grown to 210,000 tons. Marco Polo, who sailed from China to Persia on his return home, described the Mongol ships as large four-masted junks with up to three hundred crewmen and as many as sixty cabins for merchants carrying various wares. According to Ibn Battuta, some of the ships even carried plants growing in wooden tubs in order to supply fresh food for the sailors. Khubilai Khan promoted the building of ever larger seagoing junks to carry heavy loads of cargo and ports to handle them. They improved the use of the compass in navigation and learned to produce more accurate nautical charts. The route from the port of Zaytun in southern China to Hormuz in the Persian Gulf became the main sea link between the Far East and the Middle East, and was used by both Marco Polo and Ibn Battuta, among others.
En route, the ships also called at the ports of Vietnam, Java, Ceylon, and India, and in each place the Mongol representatives encountered more goods, such as sugar, ivory, cinnamon, and cotton, that were not easily produced in their own lands. From the Persian Gulf, the ships continued outside of the areas under Mongol influence to include regular trade for a still greater variety of goods from Arabia, Egypt, and Somalia. Rulers and merchants in these other areas outside the Mongol system of influence did not operate within the system of shares in the Mongol goods; instead, the Mongol authorities created long-term trading relations with them. Under Mongol protection, their vassals proved as worthy competitors in commerce as the Mongols had been in conquest and they began to dominate trade on the Indian Ocean.
To expand the trade into new areas beyond Mongol political control, they encouraged some of their vassals, particularly the South Chinese, to emigrate and set up trading stations in foreign ports. Throughout the rule of the Mongol dynasty, thousands of Chinese left home and sailed off to settle along the coastal communities of Vietnam, Cambodia, the Malay Peninsula, Borneo, Java, and Sumatra. They worked mostly in shipping and trade and as merchants up and down the rivers leading to the ports, but they gradually expanded into other professions as well.
To reach the markets of Europe more directly, without the lengthy detour through the southern Muslim countries, the Mongols encouraged foreigners to create trading posts on the edges of the empire along the Black Sea. Although the Mongols had initially raided the trading posts, as early as 1226, during the reign of Genghis Khan, they allowed the Genoese to maintain a trading station at the port of Kaffa in the Crimea, and later added another at Tana. To protect these stations on land and sea, the Mongols hunted down pirates and robbers. In the Pratica della mercatura (Practice of Marketing), a commercial handbook published in 1340, the Florentine merchant Francesco Balducci Pegolotti stressed that the routes to Mongol Cathay were “perfectly safe, whether by day or by night.”