Byzantine chant manuscripts date from the [[9th century|Ninth century]], while [[lectionary|lectionaries]] of biblical readings in [[Ekphonetic Notation ]] (a primitive graphic system designed to indicate the manner of reciting lessons from Scripture) begin about a century earlier and continue in use until the twelfth or thirteenth century. Our knowledge of the older period is derived from Church service books [[Typikon|Typika]], patristic writings and medieval histories. Scattered examples of hymn texts from the early centuries of Greek Christianity still exist. Some of these employ the metrical schemes of classical Greek poetry; but the change of pronunciation had rendered those meters largely meaningless, and, except when classical forms were imitated, Byzantine hymns of the following centuries are prose-poetry, unrhymed verses of irregular length and accentual patterns. The common term for a short hymn of one stanza, or one of a series of stanzas, is troparion (this may carry the further connotation of a hymn interpolated between Psalm verses). A famous example, whose existence is attested as early as the fourth century, is the Vespers hymn, "Phos Hilaron" ("O Gladsome Light"); another, "O Monogenes Yios" ("Only Begotten Son") ascribed to Emperor St. [[Justinian I]] (527-565), figures in the introductory portion of the Divine Liturgy. Perhaps the earliest set of troparia of known authorship are those of the [[monk]] Auxentios (first half of the fifth century), attested in his biography but not preserved in any later Byzantine order of service.