Carl Erdmann (17 November 1898 – 5 March 1945) was a German historian who specialized in medieval political and intellectual history. He is noted in particular for his study of the origins of the idea of crusading in medieval Latin Christendom, as well as his work on letter collections and correspondence among secular and ecclesiastical elites in the eleventh century. He is often mentioned alongside Percy Ernst Schramm and Ernst H. Kantorowicz as one of the most influential and important German scholars of medieval political culture in the twentieth century. His promising and remarkably prolific career was cut short by his death in the German army at the end of World War II. His grandson Martin Erdmann is a professor for experimental particle physics at the RWTH Aachen University. Education and scholarship Erdmann's curriculum vitae was not typical for a German academic of his generation. Born in Dorpat (now Tartu, Estonia) and raised in Blankenburg am Harz, Saxony-Anhalt, he initially studied to be a Lutheran minister in Berlin, but abandoned this vocation in 1919 to study history in Munich. In the wake of Germany's economic collapse in the early 1920s, however, Erdmann's family could no longer support him and he left the university to take a job as a private tutor with a wealthy German family living in Portugal. Erdmann remained in Portugal for four years and developed a deep interest in the language, history and culture of the country, particularly its medieval religious heritage. His job allowed him time to explore the archives and libraries of Lisbon and other cities, where he collected and studied enough material to form the basis of a doctoral dissertation on the history of the Crusades in medieval Portugal. In 1925, Erdmann returned to Germany and entered the University of Würzburg, where he earned his doctorate degree in 1926. Following the completion of his degree, he worked for several years at the Prussian Historical Institute in Rome (today the German Historical Institute) editing material relating to papal relations with Portugal and various other topics in church history that attracted his attention. In 1932, he submitted a manuscript at the University of Berlin on the origins of the idea of Crusade in the medieval West which earned him his Habilitation, or qualification for appointment to an academic professorship. He later expanded this thesis and published it under the title Die Entstehung des Kreuzugsgedanken (The Origins