ca. 795–800 – Tonary of St Riquier, the earliest Western source organized according to the eight Gregorian modes, borrowed from the Byzantine octoechos system
9th century – Notker the Stammerer explains the supplementary letters for neumatic notation in his Epistola ad Lantbertum
ca. 850 – Aurelian of Réôme writes the earliest extant medieval treatise on music, Musica disciplina