The Silk Road was originally built to transport silk along east-west trade routes from China to the Mediterranean. The route was built during the Han Dynasty (207 BCE – 220 CE) and played a major role in spreading cultural ideas as well. During the Mongol Empire (1206-1368), the route was re-instituted through their capital at Karakorum. The Mongols also facilitated trade by building a postal system along the trade route. Every twenty or so miles, the Mongols built a station with horses, food, and lodging that made travel along the route much easier. In addition, the Mongols promoted trade by not forcing merchants to pay confiscatory taxes. Marco Polo is believed to have been among the first travelers from Europe to use the Silk Road to travel to China.
The Mongols perfected the ancient art of making paper, and their invention spread from Samarkand west along the trade route to Eurasia. Other innovations, such as the irrigation waterwheel, also spread along the route from Syria. This invention uses pots attached to the edges of the waterwheel to lift water, and it was implemented all the way from Spain to China. As people traveled in both directions along the trade route, so did food, such as grapes from the west to the east and oranges from the east to the west. Diseases unfortunately were also spread along the route. It is believed that the Black Plague was brought to the Mediterranean from Central Asia via pelts that carried flea eggs that transmitted the plague.
By controlling the trade routes that ran from east to west, the Mongols made it much easier for goods, ideas, and even diseases to spread. The reason for this is that trade depends on stability. If the areas along trade routes are not politically stable, trade will not flourish because it will be too dangerous to trade.
Before the Mongols took their empire, the regions between China and the Middle East were not stable and trade did not flow. When the Mongols took control, they managed to make the trade routes safe and people started trading again. When this happened, it once again became easy for good things like silk and bad things like the bubonic plague to reach Europe from China.