The Book of the Eight Tones
, it is one of theliturgical books of the Orthodox Church. The Octoechos (or Paraklitiki
) covers each of the eight tones, or melodic patterns, together with its accompanying hymns, sung throughout all the services for the seven days of the week, beginning on Saturday evenings. The cycle is completed on conclusion of the eighth week and then begins anew. Yearly, the cycle of the Octoechos begins on the Sunday following Pentecost. Its origins are ascribed to the work of John of Damascus, and the formalization of the eight tones marks a watershed in Christian music, East and West.