In the ninth century, Martianus Capella’s De nuptiis Philologiae et Mercurii , a late-antique encyclopaedia of ancient learning on the seven Liberal Arts, was read with scrupulous vigour by the intellectual elite. Carolingian scholars produced a wealth of commentaries and glosses, which survived hidden in the margins of a remarkably large number of manuscripts. In the first part of this study, the manuscript tradition of the oldest commentary is taken under scrutiny, and the Carolingian reception of ancient knowledge on the subject of music is opened up and analyzed. Its relevance for the formation of a new, mediaeval music theory is evaluated. In the second part, the relevant parts of the oldest commentary are edited on the basis of eight ninth-century manuscripts.