There is evidence that, towards the close of the mediaeval period, great storms and tidal inundations occurred on the shores of the North Sea and Baltic, and in the course of these floods, culminating in 1297, the Zuider Zee was formed from a lake that existed in its neighbourhood, by the breaking down of dykes.
As a seaport its trade is now confined exclusively to the Zuider Zee.
The smaller branch to the right retains the name of Rhine and sends off another arm, called the Yssel, to the Zuider Zee.
The towns of the League, stretching from Thorn and Krakow on the East to the towns of the Zuider Zee on the West, and from Wisby and Reval in the North to Göttingen in the South, were arranged in groups, following in the main the territorial divisions.
In 1170 the land between Stavoren, Texel, and Medemblik was washed away, and a century later the Zuider Zee was formed.
