A cycle of daily devotions - the prayers of the canonical hours - performed by members of religious orders and the clergy. It originated in the services of the Jewish synagogue and in the Apostolic Church. Initially, each office consisted mainly of the recitation of Psalms and lessons from Scripture. In the fourth century, under the influence of Saint Ambrose, hymns and antiphons were added; one hundred and fifty years later, under Saint Benedict, there appeared responsories, canticles, collects, and other elaborations. By the eighth century, the cycle of eight canonical hours for the performance of the Divine Office had been fixed: matins (approximately 2:30 am), lauds (approximately 5 am), prime (approximately 6 am), terce (approximately 9 am), sext (approximately 12 noon), none (approximately 3 pm), vespers (approximately 4:30 pm), and compline (approximately 6 pm). The Divine Office was initially arranged so that the complete Psalter could be recited each week, and much of Holy Scripture throughout the year. During the Middle Ages, however, the celebration of saints' feast days and readings from their lives (see Martyrology) interfered with this structure, stimulating attempts at reform in the sixteenth century. Along with the Mass, the Divine Office forms the basis of Christian Liturgy. For a lay response to the office, see Book of Hours.