Previously unknown masterpieces by modernist painters Marc Chagall and Otto Dix are among the vast trove of works believed stolen by the Nazis and hidden in a Munich flat, an art historian said Tuesday. Meike Hoffmann, an expert aiding the investigation, said the Chagall painting, an allegorical scene dating from the mid-1920s, had a "particularly high art-historical value". The Dix work is a rare self-portrait believed to have been painted in 1919.