Kelsen's doctoral thesis on Dante's theory of the state in 1905 became his first book on political theory. In this book Kelsen made explicit his preference for the reading of Dante Alighieri's "Divine Comedy" as largely based in political allegory. The study makes a rigorous examination of the "two swords doctrine" of Pope Gelasius I, along with Dante's distinct sentiments in the Roman Catholic debates between the Guelphs and Ghibellines. Kelsen's conversion to Catholicism was contemporaneous to the book's completion in 1905. In 1908 Kelsen won a research scholarship which allowed him to attend the University of Heidelberg for three consecutive semesters, where he studied with the distinguished jurist Georg Jellinek before returning to Vienna.