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.
A notable publication by him, Studien zur Briefliteratur Deutschlands im XI. Jahrhundert (Studies on Epistolary Literature in Germany in the Eleventh Century), remains a significant contribution to the subject. His magnum opus, the critical edition of the letter collections from the reign of Henry IV, was largely completed by the early 1940s but could not be published due to wartime difficulties.