  Martin Heidegger was born in Messkirch, Germany, on September 26, 1889. Messkirch was then a quiet, conservative, religious rural town, and as such was a formative influence on Heidegger and his philosophical thought. In 1909 he spent two weeks in the Jesuit order before leaving (probably on health grounds) to study theology at the University of Freiburg. In 1911 he switched subjects, to philosophy. He began teaching at Freiburg in 1915. In 1917 he married Elfride Petri, with whom he had two sons (Jörg and Hermann) and from whom he never parted (although his affair with the philosopher Hannah Arendt, his student at Marburg in the 1920s, is well-known).