In its present (ninth-century) form the "Martyrologium Hieronymianum" gives a second feast of the Chair of St. Peter for 22 February, but all the manuscripts assign it to Antioch, not to Rome. Thus the oldest manuscript, that of Berne, says: "VIII kal. mar. cathedræ sci petri apostoli qua sedit apud antiochiam". The Weissenburg manuscript says: "Natl [natale] sci petri apostoli cathedræ qua sedit apud antiocia." However, the words qua sedit apud antiochiam are seen at once to be a later addition. Both feasts are Roman; indeed, that of 22 February was originally the more important. This is clear from the Calendar of Philocalus drawn up in the year 354, and going back to the year 311; it makes no mention of the January feast but speaks thus of 22 February: "VIII Kl. Martias: natale Petri de cathedra" (eighth day before the Calends of March, the birthday [i.e. feast] of the Chair of Peter). It was not until after the insertion of Antioch in the copies of the "Martyrologium Hieronymianum" that the feast of February gave way in importance to that of January. The Roman Church, therefore, at an early date celebrated a first and a second assumption of the episcopal office in Rome by St. Peter. This double celebration was also held in two places, in the Vatican Basilica and in a cemetery (coemeterium) on the Via Salaria. At both places a chair (cathedra) was venerated which the Apostle had used as presiding officer of the assembly of the faithful. The first of these chairs stood in the Vatican Basilica, in the baptismal chapel built by Pope Damasus; the neophytes in albis (white baptismal robes) were led from the baptistery to the pope seated on this ancient cathedra, and received from him the consignatio, i.e. the Sacrament of Confirmation. Reference is made to this custom in an inscription of Damasus which contains the line: "una Petri sedes, unum verumque lavacrum" (one Chair of Peter, one true font of baptism). St. Ennodius of Pavia (d. 521) speaks of it thus ("Libellus pro Synodo", near the end): "Ecce nunc ad gestatoriam sellam apostolicæ confessionis uda mittunt limina candidatos; et uberibus gaudio exactore fletibus collata Dei beneficio dona geminantur" (Behold now the neophytes go from the dripping threshold to the portable chair of the Apostolic confession; amid abundant tears called forth by joy the gifts of Divine grace are doubled). While therefore in the apse of the Vatican Basilica there stood a cathedra on which the pope sat amid the Roman clergy during the pontifical Mass, there was also in the same building a second cathedra from which the pope administered to the newly baptized the Sacrament of Confirmation. The Chair of St. Peter in the apse was made of marble and was built into the wall, that of the baptistery was movable and could be carried. Ennodius calls the latter a gestatoria sedes; throughout the Middle Ages it was always brought on 22 February from the above-mentioned consignatorium or place of confirmation to the high altar. That day the pope did not use the marble cathedra at the back of the apse but sat on this movable cathedra, which was, consequently, made of wood. The importance of this feast was heightened by the fact that 22 February was considered the anniversary of the day when Peter bore witness, by the Sea of Tiberias, to the Divinity of Christ and was again appointed by Christ to be the Rock of His Church. According to very ancient Western liturgies, 22 February was the day "quo electus est 1. Petrus papa" (on which Peter was first chosen pope). The Mass of this feast calls it at the beginning: "solemnitatis prædicandæ dies præcipue nobilis in quo . . . . beatus Bar-Jona voce Redemptoris fide devotâ prælatus est et per hanc Petri petram basis ecclesiæ fixus est", i.e. this day is called especially praiseworthy because on it the blessed Bar-Jona, by reason of his devout faith, was raised to pre-eminence by the words of the Redeemer, and through this rock of Peter was established the foundation of the Church. And the Oratio (collect) says: "Deus, qui hodiernâ die beatum Petrum post te dedisti caput ecclesiæ, cum te ille vere confessus sit" (O God, who didst this day give us as head of the Church, after Thyself, the Blessed Peter, etc.).
The second of the aforementioned chairs is referred to about 600 by an Abbot Johannes. He had been commissioned by Pope Gregory the Great to collect in special little phials oil from the lamps which burned at the graves of the Roman martyrs (see CATACOMBS; MARTYR) for the Lombard queen, Theodolinda. According to the manuscript list of these oils preserved in the cathedral treasury of Monza, Italy, one of these vessels had on it the statement: "oleo de sede ubi prius sedit sanctus Petrus" (oils from the chair where St. Peter first sat). Other ancient authorities describe the site as "ubi Petrus baptizabat" (where Peter baptized), or "ad fontes sancti Petri; ad Nymphas sancti Petri" (at the fountain of Saint Peter). Formerly this site was pointed out in the coemeterium majus (principal cemetery) on the Via Nomentana; it is now certain that it was on the Via Salaria, and was connected with the coemeterium, or cemetery, of Priscilla and the villa of the Acilii (Acilii Glabriones), situated above this catacomb. The foundation of this villa, showing masonry of a very early date (opus reticulatum), still exists. Both villa and cemetery, in one of whose burial chambers are several epitaphs of members of the family, or gens, of the Acilii, belong to the Apostolic Period. It is most probable that Priscilla, who gave her name as foundress to the catacomb, was the wife of Acilius Glabrio, executed under Domitian. There is hardly any doubt that the site, "ubi prius sedit sanctus Petrus, ubi Petrus baptizabat" (where Saint Peter first sat, where Peter baptized), should be sought, not in an underground cubiculum (chamber) in the catacombs, but in an oratory above ground. At least nothing has been found in the oldest part of the cemetery of Priscilla now fully excavated, referring to a cathedra, or chair.
The feast of the Cathedra Petri was therefore celebrated on the Via Salaria on 18 January; in the Vatican Basilica it was observed on 22 February. It is easy to believe that after the triumph of Christianity the festival could be celebrated with greater pomp in the magnificent basilica erected by Constantine the Great over the confessio, or grave of Peter, than in a chapel far distant from the city on the Via Salaria. Yet the latter could rightly boast in its favour that it was there Saint Peter first exercised at Rome the episcopal office ("ubi prius sedit sanctus Petrus", as Abbot Johannes wrote, or "qua primo Rome petrus apostolus sedit", as we read in the "Martyrologium Hieronymianum" at 18 January). This double festival of the Chair of St. Peter is generally attributed to a long absence of the Apostle from Rome. As, how ever, the spot, "ubi s. Petrus baptizabat, ubi prius sedit" was distant from the city, it is natural to think that the second feast of the cathedra is connected with the opening of a chapel for Christian worship in the city itself. Source: The Catholic Encyclopedia