of the Idea of Crusading) in 1935. In the meantime, Erdmann was recruited by the Monumenta Germaniae Historica (MGH), the prestigious historical institute dedicated to the critical editing and publishing of sources relating to German history in the medieval period. As an academic researcher (wissenschaftlicher Mitarbeiter) at the MGH, Erdmann was assigned the task of preparing editions for a number of important manuscript letter collections from the eleventh century relating to the history of the Investiture Controversy and Gregorian Reform. During this period, Erdmann made a number of critically important contributions to the study of epistolary literature in the Middle Ages and the role letters exchanged among bishops, abbots, kings and other elites played in communicating political ideas. His 1938 monograph, Studien zur Briefliteratur Deutschlands im XI. Jahrhundert (Studies on Epistolary Literature in Germany in the Eleventh Century) remains a classic on the subject. His final masterpiece, the critical edition of the letter collections from the reign of Henry IV, was largely completed by the early 1940s, but could not be printed due to wartime difficulties. It was finally sent to press by the MGH in the 1950s. Political problems and military service Under normal circumstances, a position at the MGH would have led to a prestigious university chair in medieval history within a few years and no-one doubted that Erdmann was the brightest rising young star in his field. However, in 1933, and particularly after 1935, German academic institutions and universities began to implement political controls in line with the policies of the new Nazi government. Although Erdmann continued to work at the MGH, his liberal views and refusal to join or endorse the Nazi Party effectively blacklisted him from further academic advancement, particularly at the university level. Furthermore, his book on the Crusades had been a thinly-veiled critique of a political value system that raised war and imperialism to the level of a religious creed. During the late 1930s and early 1940s, Erdmann's research on the early Saxon monarchs of Germany (the Ottonians) also dissented from the politically correct orthodoxy, raising questions about the rise and rule of a dynasty which figured prominently in Nazi historical propaganda. Towards the end of 1943, Erdmann was conscripted into the Wehrmacht and the administration of the MGH, by now in the hands of academics friendly to the Nazi regime, declined to intervene on his behalf. He was trained as an Italian