Hagiopolitan Octoechos

Oktōēchos (here transcribed "Octoechos"; Greek: ὁ Ὀκτώηχος pronounced in koine: Greek pronunciation: [okˈtóixos]; from "eight" and "sound, mode" called echos; Slavonic: Осмогласие, Osmoglasie from "eight" and "voice, sound") is the name of the eight mode system used for the composition of religious chant in Byzantine, Syriac, Armenian, Georgian, Latin and Slavic churches since the Middle Ages. In a modified form the octoechos is still regarded as the foundation of the tradition of monodic Orthodox chant today (Neobyzantine Octoechos).

The Octoechos as a liturgical concept which established an organization of the calendar into eight-week cycles, was the invention of monastic hymnographers at Mar Saba in Palestine and in Constantinople. It was formally accepted in the Quinisext Council of 692, which also aimed to replace the exegetic poetry of the kontakion and other homiletic poetry, as it was sung during the morning service (Orthros) of the cathedrals.

One reason why another eight mode system was established by Frankish reformers during the Carolingian reform, may well have been that Pope Adrian I accepted the seventh-century Eastern reform for the Western Church as well during the 787 synod. The only evidence for this is an abbreviated chant book called a "tonary". It was a list of incipits of chants ordered according to the intonation formula of each church tone and its psalmody. Later on, fully notated and theoretical tonaries were also written.

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