A leading scholar of the music of Ancient Greece, Mathiesen has written four monographs and numerous articles on the topic.
At the latter school, Mathiesen's teachers included scholars such as Ingolf Dahl and Halsey Stevens.
[1] His scholarship includes the topics of "textual criticism, editorial technique, bibliography and codicology".
[1] Mathiesen established in 1990 the online project Thesaurus Musicarum Latinarum (TML) and led it until 2015.
Due to his efforts TML became a world-wide known database of early music treatises, with a free access.