German philosophers have helped shape western philosophy from as early as the Middle Ages (Albertus Magnus). Later, Leibniz (17th century) and most importantly Kant played central roles in the history of philosophy. Kantianism inspired the work of Schopenhauer and Nietzsche as well as German idealism defended by Fichte and Hegel. Engels helped develop communist theory in the second half of the 19th century while Heidegger and Gadamer pursued the tradition of German philosophy in the 20th century. A number of German intellectuals were also influential in sociology, most notably Adorno, Habermas, Horkheimer, Luhmann, Simmel, Tönnies, and Weber. The University of Berlin founded in 1810 by linguist and philosopher Wilhelm von Humboldt served as an influential model for a number of modern western universities.