Before the fall of the West Roman Empire in 476, Roman towns stood along and near the Rhine and Danube rivers. These towns were centers of trade. They included what are now Bonn, Cologne, Regensburg, Trier, and Vienna. After the fall of Rome, these towns almost disappeared. Trade gradually resumed under the Saxon and Salian emperors. Some of the old towns grew again, and new ones appeared around the castles of princes and bishops. Many cities became so large and rich that they gained self-rule.

When the emperors began losing power, the cities could not rely on outside help in case of attack. The more prosperous cities banded together into leagues and formed their own armies for protection. The strongest league was the Hanseatic League, which began to develop in the late 1100's. It included Cologne, Dortmund, and the major ports of Bremen, Hamburg, and Lubeck. It became a great commercial and naval power in the North and Baltic seas during the 1300's.