The breviary is the result of a long compression. The office was originally choral and communal, sung from a shelf of books: psalter, antiphonary, hymnal, lectionary, collectar, each held by different hands. The word breviarium, an abridgement, appears from around the eleventh century for compilations that drew the essentials into one volume, and the decisive push came in the thirteenth, when the friars of the new mendicant orders, always on the road, adopted the compact office of the papal curia and carried it across Europe. A portable office made a portable clergy possible. After Trent, Pius V issued the reformed Roman Breviary of 1568, suppressing recent accretions and imposing a single standard on the Latin Church with the same exceptions allowed to the missal.
Later centuries tinkered; the most consequential change came under Pius X in 1911, when the ancient arrangement of the psalter, which had loaded enormous blocks of psalmody onto certain hours, was redistributed so that the week's burden fell more evenly. The Second Vatican Council then authorized the deepest recasting since Trent: Prime was suppressed, the psalter spread over four weeks, the readings enriched, and the reformed book issued in 1971 under the name Liturgy of the Hours. Anglicanism had compressed further still in 1549, folding the monastic hours into the two offices of Morning and Evening Prayer in the Book of Common Prayer, a reminder that the breviary's history is one long negotiation between the ideal of ceaseless prayer and the hours a human day actually contains.