Night prayer before sleep is as old as Christian devotion, but Compline as a distinct office belongs to the monastic legislators. The Rule of St Benedict in the sixth century prescribes it exactly: three psalms said straight through without antiphons, the hymn, a lesson, the blessing, and after it the rule of silence, enforced with penalties, that turned the monastery's night into a fast of speech. Liturgical historians debate how much Benedict invented and how much he codified from the practice of his age, with the office's roots visible in the prayers before sleep that Basil and Chrysostom already commend; what is certain is that the Benedictine shape carried the hour through the Western Middle Ages, gathering the enrichments that became its identity, the Nunc Dimittis, the Marian anthems sung after it in season, and the confession of sins at its head.
The Reformation folded Compline into Anglican Evening Prayer, but the office refused to disappear: the 1928 English proposals and the modern prayer books restored it, and sung Compline by candlelight has become, unexpectedly, one of the most successful late-modern liturgical revivals, drawing students and seekers to cathedrals and college chapels for a service of plainchant, darkness and silence with no sermon and no demand. The Byzantine tradition keeps its own parallel, the apodeipnon, after-supper, with a Great Compline for Lent whose refrain God is with us rolls through the night services of the fast. Last of the hours to form, Compline has proven the hardest to kill: the day insists on ending, and the office owns the ending.