meteorological unit on the western front". Heidegger taught courses at the University of Freiburg from 1919-1923. See his published courses in Gesamtausgabe. Early Freiburg lecture courses, 1919–1923. Marburg In 1923, Heidegger was elected to an extraordinary professorship in philosophy at the University of Marburg. His colleagues there included Rudolf Bultmann, Nicolai Hartmann, Paul Tillich, and Paul Natorp. Heidegger's students at Marburg included Hans-Georg Gadamer, Hannah Arendt, Karl Löwith, Gerhard Krüger, Leo Strauss, Jacob Klein, Günther Anders, and Hans Jonas. Following on from Aristotle, he began to develop in his lectures the main theme of his philosophy: the question of the sense of being. He extended the concept of subject to the dimension of history and concrete existence, which he found prefigured in such Christian thinkers as Paul of Tarsus, Augustine of Hippo, Martin Luther, and Søren Kierkegaard. He also read the works of Wilhelm Dilthey, Husserl, Max Scheler, and Friedrich Nietzsche. Freiburg In 1927 Heidegger published his main work, Sein und Zeit (Being and Time). When Husserl retired as Professor of Philosophy in 1928, Heidegger accepted Freiburg's election to be his successor, in spite of a counter-offer by Marburg. Heidegger remained at Freiburg im Breisgau for the rest of his life, declining later offers including one from Humboldt University of Berlin. His students at Freiburg included Hannah Arendt, Günther Anders, Hans Jonas, Karl Löwith, Charles Malik, Herbert Marcuse, and Ernst Nolte. Karl Rahner likely attended four of his seminars in four semesters from 1934 to 1936. Emmanuel Levinas attended his lecture courses during his stay in Freiburg in 1928, as did Jan Patočka in 1933; Patočka in particular was deeply influenced by him. Heidegger was elected rector of the University on 21 April 1933, and joined the Nazi Party on 1 May. During his time as rector he was a member and an enthusiastic supporter of the party. There is continuing controversy as to the relationship between his philosophy and his political allegiance to Nazism. He wanted to position himself as the philosopher of the party, but the highly abstract nature of his work and the opposition of Alfred Rosenberg, who himself aspired to act in that position, limited Heidegger's role. His withdrawal from his position as rector owed more to his frustration as an administrator than to any principled opposition to the Nazis, according to historians. In his inaugural address as rector on 27 May he expressed his support