When was written music first developed?
Musical notation
The term 'graphic notation' refers to the contemporary use of non-traditional symbols and text to convey information about the performance of a piece of music. Practitioners include Christian Wolff, Earle Brown, Anthony Braxton, John Cage, Morton Feldman, Krzysztof Penderecki, Cornelius Cardew, and Roger Reynolds. See Notations, edited by John Cage and Alison Knowles, ISBN0-685-14864-5.