The foundations of the Hanseatic League, an alliance of trading cities that for a time in the later Middle Ages and the Early Modern period maintained a trade monopoly over most of Northern Europe and the Baltic, can be seen as early as the 12th century. At about this time, merchants in a given city began to form societies, or Hansa, with the intention of trading with foreign cities. These societies worked to acquire special trade privileges for their members. For example, the merchants of Cologne were able to convince Henry II of England to grant them special trading privileges and market rights in 1157.
Eventually, the capital of Hansa were moved to Polish main port of Danzig. Other important Polish cities, members of Hansa were Thorn, Elbing and Krakow.
The League was fluid in nature, but its members shared some traits. First, most of the Hanseatic League (or Hansa) cities either were founded as independent cities or gained independence through the collective bargaining power of the League. Independence in this case was limited; it meant that the cities owed allegiance directly to the Emperor, without any intermediate tie to the local nobility. Another similarity was that the cities were all strategically located along trade routes. In fact, at the height of its power, the merchants of the Hanseatic League were sometimes able to use their economic power (and sometimes their military might -- trade routes needed protecting, and the League's ships were well-armed) to influence Imperial policy. The League also wielded power abroad: between 1368 and 1370, the League's ships fought against the Danes, and forced the Danish king to grant the League 15 percent of the profits from Danish trade (Treaty of Stralsund).
Exclusive trade routes often came at a high price. In most foreign cities, the Hansa traders were confined to certain trading areas and to their own trading posts. They were seldom, if ever, allowed to interact with the local inhabitants, except in the matter of actual negotiation. Moreover, the power of the League was envied by many, merchant and noble alike. The very existence of the League and its privileges and monopolies created economic and social tensions that often crept over into rivalry between League members. By the late 16th century, the League had all but imploded, unable to deal with its own internal struggles, the social and political changes that accompanied the Reformation, the rise of Dutch and English merchants and the incursion of the Ottoman Turks upon its trade routes and the Empire itself.
Despite its demise, several cities still maintain the link to the Hanseatic League. Even in the 21st century, the cities of Deventer, Kampen, Zutphen, Lübeck, Hamburg, Bremen, Rostock, Wismar, Stralsund, Greifswald and Anklam call themselves Hansa cities. For Lübeck in particular, this anachronistic tie to a glorious past remained especially important in the second half of the 20th century.