The article explores an interdisciplinary conjunction of music, literature and modernism. I examine the relationship between aspects of early music scholarship and modernism, with specific reference to Ezra Pound’s critical and editorial work on medieval song, and to the composition, in the 1920s, of his modernist opera Le Testament. This analysis places Pound’s work as editor and composer not only in the context of recent critical reflections on the idea of authenticity, but also in relation to the histories and methodologies of medieval music interpretation. First, in drawing attention to Pound’s much–neglected collaborative edition of medieval songs entitled Hesternae Rosae, I contextualise his experiments in rhythmic reconstruction with reference to early and late twentieth-century musicologists working in this field. I make particular reference to the work of Pierre Aubry and rhythmic mode theory, and the later perspectives of Hendrik van der Werf. Secondly, I proceed to analyse Pound’s monophonic and dance song compositions in Le Testament, exploring the way in which serious medieval musicological scholarship prepared for, and is allied to, the development of a rhythmically and dramatically complex musical style.