Sea Ice Conditions in Gulf of Gdansk in 15 century 
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Majority of the cities in Poland, including Krakow, belonged to Hanza. For this reason, Gulf of 
Gdansk with estuary of biggest Polish river: Wisla - was important navigation area in the Baltic 
Sea. 
Fig. 2. Navigation on the Baltic Sea in 15 and 16 centuries (Atlas Historyczny) 
Sea ice conditions in Gulf of Gdansk and severity of winters is presented in a form of table 
extracts from historical sources (for example Table 2). The following division into 3 parts has 
been performed: the first contains information concerning freezing the Gulf of Gdansk and 
additionally on severity of winters in Poland; in the second one there are presented extracts 
from sources referring to freezing the Danish Straits, the Baltic Sea and the European countries 
and in the third one there is included the calendar of history of Hanza. It was a meaning source 
of knowledge as well nevertheless of indirect character. 
Sea ice conditions reconstruction was to present them in numerical form, applying 3 degree 
scale (1 - very mild; 3 - severe and very severe; 2 - others). In case of sea ice conditions in the 
Gulf, the determination of very mild and very severe winter could be done with very high 
probability. It was very difficult to separate mild winters (lacking of 1-3 days with sea ice on the 
main fairways) or normal (ice cover in shallow bays and lagoons). The results of studies are 
presented in Fig.3.