Low Prussian (German: Niederpreußisch), sometimes known simply as Prussian (Preußisch), is a dialect of East Low German that developed in East Prussia. Low Prussian was spoken in East and West Prussia and Danzig up to 1945. It developed on a Baltic substrate through the influx of Dutch- and Low-German-speaking immigrants. It overruled Old Prussian, which then became extinct in the 17th century.Plautdietsch, a Low German variety, is included within Low Prussian by some observers.