Traditional Roman Breviary
By the end of the 5th century, the Liturgy of the Hours was composed of seven offices. Of these seven, Compline seems to have been the last to appear, because the 4th century Apostolic Constitutions VIII iv 34 do not mention it in the exhortation "Offer up your prayers in the morning, at the third hour, the sixth, the ninth, the evening, and at cock-crowing".[7] An eighth office, Prime, was added by Benedict of Nursia in the 6th century. These eight are known by the following names, which do not reflect the times of the day at which in the second millennium they were traditionally recited, as shown by the use of the word "noon", derived from Latin (hora) nona,[8][9] to mean midday, not 3 in the afternoon: * Matins (during the night, at midnight with some); also called Vigils or Nocturns or, in monastic usage, the Night Office * Lauds or Dawn Prayer (at Dawn, or 3 a.m.) * Prime or Early Morning Prayer (First Hour = approximately 6 a.m.) * Terce or Mid-Morning Prayer (Third Hour = approximately 9 a.m.) * Sext or Midday Prayer (Sixth Hour = approximately 12 noon) * None or Mid-Afternoon Prayer (Ninth Hour = approximately 3 p.m.) * Vespers or Evening Prayer ("at the lighting of the lamps", generally at 6 p.m.) * Compline or Night Prayer (before retiring, generally at 9 p.m.)
This arrangement of the Liturgy of the Hours is attributed to Saint Benedict. However, it is found in Saint John Cassian's Institutes and Conferences,[10] which describe the monastic practices of the Desert Fathers of Egypt.
Liturgy of the Hours of Paul VI

Benedictine monks sings Vespers on Holy Saturday.
After the Second Vatican Council, Pope Paul VI promulgated a new Roman Breviary, commonly referred to as "Liturgy of the Hours". The structure of the offices, the distribution of psalms, and the prayers themselves were modified. Prime was suppressed entirely. In short, the burden was lessened. "Major" and "minor" hours were defined: * The Officium lectionis, or Office of Readings, (formerly Matins) — major hour * Lauds or Morning prayer — major hour * Daytime prayer, which can be one or all of: * Terce or Mid-Morning Prayer * Sext or Midday Prayer * None or Mid-Afternoon Prayer * Vespers or Evening Prayer — major hour * Compline or Night Prayer
All hours, including the minor hours, start with the versicle from Ps 70 (69) v. 2[11] (as do all offices in the traditional Breviary except Matins and Compline): "V. Deus, in adiutorium meum intende. R. Domine, ad adiuvandum me festina" (God, come to my assistance; Lord, make haste to help me), followed by the doxology. The verse is omitted if the hour begins with the Invitatory (Lauds or Office of Reading). The Invitatory is the introduction to the first hour said on the current day, whether it be the Office of Readings or Morning Prayer.
The opening is followed by a hymn. The hymn is followed by psalmody. The psalmody is followed by a scripture reading. The reading is called a chapter (capitulum) if it is short, or a lesson (lectio) if it is long.
The reading is followed by a versicle. The hour is closed by an oration followed by a concluding versicle. Other components are included depending on the exact type of hour being celebrated. In each office, the psalms and canticle are framed by antiphons, and each concludes with the traditional Catholic doxology.