Ordo Romanus is the name given to every rule of the Romish Church in general, and particularly to the rules concerning worship. Like τάξις, διάταξις, the rule and its exposition, or τακτικός (τακτική sc. βίβλος,), or ordo or ordinarius (sc. liber), or ordinale and ordinalis' (sc. liber) (Du Fresne), signifies a collectioii of rules for worship. In the course of time there appeared many such libelli, which in so far as they related to the same subject, were compiled together. The exact time when these different libelli appeared is not ascertanined, nor that of their compilation. As early as the 5th century there was a distinction between the sacramentarium, containing the prayers for the Eucharist, the antiphonarius (liber), with the liturgic chants, and finally the ordo, constituting the ritual. See F. Probst, Verwaltung d. hochheiligen Eucharistie (Tiibing, 1853), p. 9 sq.
Various ordines appeared in the different churches, but they were gradually all superseded by the Roman ordo, for the popes as early as the 5th century used every exertion to have the worship conducted everywhere according to the usages of Rome. The subsequent publishers of rituals often confounded the Roman with other rituals, hence the number of those which were published. See Mabillon, In Ordinem Romanum commentarius, preceding his edition of the Atiqui libri rituales sanctae Romanae ecclesiae, in the Museum Italicum, t. ii (Paris, 1724, 4to). The oldest Ordo Romanus is attributed to bishop Gelasius († 496) by Mabillon (as above) and Muratori, Liturgia Romana vetus (Venice, 1748), 1:289 sq. Yet from the Epist. I of Innocent I, Ad Decentium, in 416 (in cap. 11, dist. 11), there appears to have existeld an older ordo. which is now lost. The ordo attributed to Gelasius, although it often refers to Leo I, seems to have been written by an unknown author in the time of Felix III, the predecessor of Gelasins (Bahr, D. christlich-ronmische Theologie, p. 364). This ordo, as well as that published by Mabillon annd Muratori as No. 1, was in general use in the 9th century, as is proved by the use made of it by Amalarius. These two ordines, together with those published as Nos. 3 and 4 by Mabillon, and which are of somewhat later date, treat of the missa potificalis. The ordines 5 to 10 of Mabiilon, which are of much later origin, aind belong probablly in part at least to the 11th century, refer to the missa episcopalis, the ordo scutinii ad electos, qualiter debeat celebrari (in baptism), the forms of ordination from the different degrees, as also the ordo, qualiter agendum sit quinta feria in cesna Domi, feria sexta. Parasceve, in sabbato stincto, ad-reconciliandum poenitentem, ad visitandunm infirmlum, ad consignandum pueros-sive iinfntes, ad ungendum infiimos, ad coinmunicandum- infirmos, ordo sepeliendi cle- icos Romance fraternitatis. We now possess but fragments of most of these ordines. It is therefore doubtful whether Bernard of Pavia, who quotes numerous passages of the Ordo Romanus in his Breviarnium Extravagantium (which are also given in the collection of decretals of Raymundus a Pennaforte, c. 9, De officio archidiaconi,1, 23; c. 9, De officio-primicerii 1; 25; c. 9. De officio custodis,1, 27), obtained or obrrowed them from an ancient Ordo Romanus or from a later one. At any rate, those passages are not to be found in any of the printed ordines.
Among the oldest published Ordines Romani are those of George Cassander (Colon. 1559,1561; also in his works, Paris, 1616), Melchio Hittorp (Colon. 1568). and G. Ferrarius (Romans 1591; Paris, 1610, 1624. fol.). About 1143 Benedict, a canon and chorister of St. Peter's, compiled an ordo entitled Liber pollicitus ad Guidonem de Castello (the fiuture pope Celestine II, then cardinal of St. Marc). He describes the divine worship forn the whole ecclesiastical year, with special reference to the papal affairs (published in Mabillon, No. 11). At the Council of Pavia, in 1160; the clergy made use of aliber de vita et ordinatione Romanorum pontificum (Pertz, Monumenta Germ. 4:126). The Ordo Romanus contained also the forms to be used at the coronation of the emperor. On the form used in 1192 see Pertz. (p. 187 sq.), Mabillon, and Martene. This form was adopted inn the ordo written in 1192 by cardinal Cencius (Mabillon, No. 12). Since the 13th century the expression Ceremoniale Romanum seems to have gradually taken the place of that of Ordo Romanus. Gregory X (1272) caused a new one on the election and the functions of popes to be compiled (Mabillon, No. 13). A subsequent one appeared in the middle of the 14th century (Mabillon, No. 14), which Mabillon attributes to cardinal Gaietanus. One on the ecclesiastical functions of the Roman clergy was compiled by Petrus Amelius, bishop of Sinigaglia († 1398); a larger work of the same kind, by Augustinus Piccolomini, was published at Venice in 1516, with the sanction of Leo X under the title of Rituum ecclesiasticorum sive sacrarum ceremoniarum libri tre. The Pontificale Romanum of Clement VIII (1596), and his Ceremoniale Episcoporum (1600, often reprinted and revised) have finally taken the place of the old Ordines Romani. At present there is an ecclesiastical calendar published each year in every diocese, which fills the place of an Ordo Romanus, and generally bears the title Ordo offici divini juxta ritum Romanum, or Juxtan rubricas breviarii et missalis Romani atqque denreta sacrae rituum congregationis.
See Hoffmann, Nova scriptorum ac monumentorum collectio, 2:16 sq. (Leips. 1733, 4to); Rheinwald, Ordo Romanus, in Ersch u. Gruber, Allgem, Encyklopadie, sec. iii, pt. v; Herzog, Real-Encyklop. 9. 693 sq. (J.N. P.)