Franco of Cologne (; also Franco of Paris) was a German music theorist and possibly a composer. He was one of the most influential theorists of the Late Middle Ages, and was the first to propose an idea which was to transform musical notation permanently: that the duration of any note should be determined by its appearance on the page, and not from context alone. The result was Franconian notation, described most famously in his Ars cantus mensurabilis. Life Some details are known about his life, and more can be inferred. In his own treatise he described himself as the papal chaplain and the preceptor of the Knights Hospitallers of St. John at Cologne, an extremely powerful position in northern Europe in the 13th century. Other documents of the time refer to him as "Franco of Paris" as well as "Franco teutonicus"; since his writing on music is intimately associated with the Notre Dame school of Paris, and his Teutonic origin is mentioned in several sources, he was probably German, probably traveled between Cologne and Paris, which had close relations during that time, and probably had a musical position at Notre Dame at some point, perhaps as a teacher, composer or singing master. Jacques of Liège, in his early 14th century Speculum musice, a passionate defense of the 13th century ars antiqua style against the new "dissolute and lascivious" ars nova style, mentioned hearing a composition by Franco of Cologne, a motet in three voices. No music of Franco with reliable attribution has survived, although some works of the late 13th century, from Parisian sources but stylistically resembling German music of the time, have on occasion been attributed to him. Writings Franco's most famous work was his Ars cantus mensurabilis, a work which was widely circulated and copied, and remained influential for at least 200 years. Unlike many theoretical treatises of the 13th century, it was a practical guide, and entirely avoided metaphysical speculations; it was evidently written for musicians, and was full of musical examples for each point made in the text. The topics covered in the treatise include organum, discant, polyphony, clausulae, conductus, and indeed all the compositional techniques of the 13th century Notre Dame school. The rhythmic modes are described in detail, although Franco has a different numbering scheme for the modes than does the anonymous treatise De mensurabili musica on the rhythmic modes, written not long