Besides the princes and knights, there is a very important [Sidenote: The imperial cities.] body of tenants-in-chief—the _Reichstädte_, or imperial cities. These had risen to importance, partly through the economic conditions which gave them wealth, and partly through the policy of several of the Emperors, who had encouraged the growth of municipal life as a source of revenue and as a check upon the power of the princes. German cities may be divided roughly into two great groups: those in the south, like Augsburg, Nürnberg, Ratisbon, etc., which obtained importance from their position on the great commercial routes leading from Venice and Genoa to different parts of Europe; and those in the north, on the Baltic and the German Ocean, whose function was to carry on the trade between the east and the west of Northern Europe, and to exchange at Bruges the products of the north for the commodities brought by the southern merchants (see p. 422). The strength of the towns lay in their wealth and their walls; their weakness in their isolation and mutual jealousy. This weakness the southern cities never overcame; their leagues for common objects were never durable, and therefore never effectual. But the northern towns were left more to themselves: they came into contact with less developed states, and they were subject to the pressure of more constant and more immediate political interests. The necessity of securing trade privileges in the countries lying to the east and west of the Baltic, and the duty of defending their commercial routes against the aggressive Scandinavian state of Denmark, which commanded the outlets from the Baltic, forced the northern towns into a semi-federal union, and the Hanseatic League became for a time a great political power in the north. In the end the northern cities also succumbed, owing mainly to a great change in trade routes, and partly to the growing predominance of the princes. But at the beginning of this period the future destiny of the German towns was unknown, and to contemporaries it seemed quite possible that cities like Nürnberg and Augsburg, or Lübeck and Hamburg, might obtain an independence and a power not markedly inferior to that which was actually acquired at this time by Venice and Florence, which were in theory equally tenants-in-chief of the Empire, though further removed from the exercise of imperial authority.