Director of the Städtische Kunstsammlungen Breslau (Municipal Art Collections Breslau) and Nazi art ideologue. After the German attack on Poland in 1939, Barthel collaborated with the head Nazi art plundering in Poland, Kajetan Mühlmann (q.v.) to write Nazi-ideological books on Polish culture, making the argument that Poland was really part of Germany. During the Third Reich years, Barthel participated in art looting in Poland and co-authored the catalogue "Secured Works of Art in the General Government" that listed cultural assets that had been confiscated in Poland. He took advantage of his relationships to Jewish private collectors to acquire their works inexpensively. Barthel's Polish art histories, justifying the looting of Polish art treasures and Germany's conquering Poland fell into a larger movement in German art literature, most notably the book by Dagobert Frey (q.v.) on Krakau, 1941, where Frey decline to identify Cracow as a Polish city.
andMühlmann, Kajetan. Sichergestellte Kunstwerke im Generalgouvernement [printed by andMühlmann?], 1940?; andMühlmann, Kajetan. Krakau: Hauptstadt der deutschen Generalgouvernements Polen: Gestalt und künstlerische Leistung einer deutschen Stadt im Osten. Breslau: Korn Verlag, 1940.
"Raub und Resitution" Jüdisches Museum Berlin (exhibition webpage) http://www.jmberlin.de/raub-und-restitution/en/home.php