OCTAVARIUM ROMANUM. - Liturgical book of the Roman Church, of optional use, which contains the lessons of the second and third Nocturn to be read during the days of the particular octaves of the feasts of the patrons and titulars of churches.
Once the norms for the celebration of the particular octaves of the patrons and titulars of churches had been definitively established by St. Pius V, with the publication of the reformed Breviary (1568) and Missal (1570), the lack of proper lessons for the current days of these octaves was felt, since such lessons are missing in the body of the Breviary. To remedy this defect, the well-known liturgist Gavanto, consultor of the Sacred Congregation of Rites, set to work and composed a collection of patristic readings, arranged specifically for the days of these particular octaves. The doubt then arose whether such a collection should enter directly into the Breviary, or form a separate liturgical book. The Sacred Congregation resolved to publish a book separate from the Breviary, and confirmed this decision with the decree of 19 Feb. 1622, prefixed to the book which received the name: O. R., published in 1623 in Rome and almost immediately also abroad in various editions. Gavanto prefixed to it an erudite introduction, in which he dwells at length on the history and meaning of the octaves, an introduction that has remained in modern editions. The last two editions of the O. R. are those of Pustet, edited by the same Sacred Congregation of Rites, in 1882 and 1902, with an ample appendix.
The O. R. is not strictly obligatory, but, to a doubt put to it, the Sacred Congregation of Rites replied that the lessons missing for the particular octaves "desumantur ex O. R." (Decr. auth. n. 2735; 8 Aug. 1835).