A vast amount of information about trade routes in medieval times has been summarized in a wonderful new map by Martin Jan Mansson. The graphic at left is just an excerpt. The full map covers Europe, Africa and Asia. Check it out here.
The map has an incredible level of detail and is completely zoomable. It includes major and minor locations, major and minor routes, sea routes, canals and roads. Its maker explains that:
"Even before modern times the Afro-Eurasian world was already well connected. This map depicts the main trading arteries of the high middle ages, just after the decline of the Vikings and before the rise of the Mongols, the Hansa and well before the Portuguese rounded the Cape of Good Hope."