Page "Old Prussian language" Paragraph 3

In addition to Prussia proper the original territory of the Old Prussians may also have included eastern parts of Pomerelia ( some parts of the region east of the Vistula River ).

The language may have also spoken much further east and south in what became Polesia and part of Podlasia with the conquests by Rus and Poles starting in the 10th century and by the German colonisation of the area which began in the 12th century.

According to the archaeologist Marija Gimbutas, the entire area has thousands of river names that can be traced back to an original Baltic language, even though they have undergone Slavicization.