From 'Catholic Encyclopedia': The Goths, who conquered and pillaged Rome in 410, advanced toward the city by the Via Salaria and the Via Nomentana; the same roads were traversed in the sixth and seventh centuries by later German invaders of Roman territory. Not only the churches, therefore, but even the cemeteries on these thoroughfares were easily given to plunder and devastation. We have seen, moreover, that as late as 600 a lamp was burning on the site "ubi prius sedit sanctus Petrus". If the original chair of the Apostle had still been there at that time, would it have been saved from destruction in the pillage that did not spare the sarcophagi in the catacombs? The words of the Abbot Johannes, "oleo de sede, ubi prius sedit sanctus Petrus", seem to leave scarcely a doubt as to this. The fact, evidenced by the martyrologies (see above), that by the ninth century one of the two feasts of the Roman cathedra had drifted away to Antioch, shows that the cathedra of the Via Salaria must have perished as early as the sixth or seventh century.
We come now to the question, where stood originally the chair shown and venerated in the Vatican Basilica during the fourth century? On the strength of ancient tradition it has been customary to designate the church of Santa Pudenziana as the spot where, in the house of the supposed Senator Pudens, the two great Apostles not only received hospitable entertainment, but also held Christian services. But the legends connected with Santa Pudenziana do not offer sufficient guarantee for the theory that this church was the cathedral and residence of the popes before Constantine. At the close of his Epistle to the Romans (xvi, 5), St. Paul mentions a place where religious services were held, the house of Aquila and Prisca (ten kat oikon auton ekklesian — now Santa Prisca on the Aventine). Aquila and Prisca are first among the many to whom the Apostle sends salutations. Aquila's connexion with the Catacomb of Priscilla is still shown by the epitaphs of that burial place. In 1776 there was excavated on the Aventine, near the present church of Santa Prisca, a chapel with frescoes of the fourth century; in these frescoes pictures of the two Apostles were still recognizable. Among the rubbish was also found a gilded glass with the figures of Peter and Paul. The feast of the dedication of this church (an important point) still falls on the same day as the above-described cathedra feast of 22 February; this church, therefore, continued to celebrate the traditional feast even after the destruction of the object from which it sprang. In the crypt of Santa Prisca is shown a hollowed capital, bearing in thirteenth-century letters the inscription: BAPTISMUS SANCTI PETRI (Baptism of Saint Peter), undoubtedly the echo of an ancient tradition of the administration of baptism here by Peter. In this way we have linked together a series of considerations which make it probable that the spot "ubi secundo sedebat sanctus Petrus" (where Saint Peter sat for the second time), must be sought in the present church of Santa Prisca; in other words, that the chair referred to by St. Damasus was kept there in the period before Constantine. It was there, consequently, that was celebrated the "natale Petri de cathedrâ", set for 22 February in the calendars beginning with the year 354. It follows also that this is the cathedra referred to in the oldest testimonia which speak of the chair from which Peter taught at Rome. The (third-century) poem, "Adversus Marcionem", says (P.L., II, 1099):
Further, St. Cyprian, writing about 250, during the vacancy of the chair after the death of Pope St. Fabian, describes it as follows: "Cum locus Fabiani, id est locus Petri et gradus cathedræ sacerdotalis vacaret" (when the place of Fabian, i.e. the place of Peter and the step of the sacerdotal chair were vacant). Still earlier, about 200, Tertullian writes, in his "De præscriptione bæreticorum": "Percurre ecclesias apostolicas, apud quas ipsæ adhuc cathedræ apostolorum suis locis præsident. Si Italiæ adjaces habes Romam" (Visit the Apostolic churches in (among) which the very chairs of the Apostles still preside in their places. If you are near Italy, there is Rome).
How Pope Damasus might be led to transfer the cathedra Petri from Santa Prisca to the Vatican, can be readily understood from the circumstances of that time. From the reign of the first Constantine the Lateran had been the residence of the popes, and its magnificent basilica their cathedral, while the neighbouring baptistery of Constantine served for the solemn administration of baptism on the eve of Easter. In the half-century from 312 to 366 (date of the accession of Damasus), the importance of Santa Prisca, its baptistery, and its cathedra must naturally have declined. Damasus could therefore be certain of the approval of all Rome when he transferred the venerable Apostolic relic from the small chapel in Santa Prisca to his own new baptistery in the Vatican, where it certainly remained to the first quarter of the sixth century, after which it was kept in different chapels of the Vatican Basilica. During the Middle Ages it was customary to exhibit it yearly to the faithful; the newly-elected pope was also solemnly enthroned on this venerable chair, a custom that ceased at the transfer of the papal capital to Avignon, in the early part of the fourteenth century. In order to preserve for posterity this precious relic, Alexander VII (1655-67) enclosed, after the designs of Bernini, the Cathedra Petri above the apsidal altar of St. Peter's in a gigantic casing of bronze, supported by four Doctors of the Church (Ambrose, Augustine, Athanasius, Chrysostom). Thenceforth, for 200 years, it was not exhibited to the public. In 1867, however, on the occasion of the eighteenth centenary of the martyrdom of the two great Apostles, it was exposed for the veneration of the faithful. At that time the Alessandri brothers photographed the chair, and that photograph is reproduced here. The seat is about one foot ten inches above the ground, and two feet eleven and seven-eighths inches wide; the sides are two feet one and one-half inches deep; the height of the back up to the tympanum is three feet five and one-third inches; the entire height of the chair is four feet seven and one-eighth inches. According to the examination then made by Padre Garucci and Giovanni Battista de Rossi, the oldest portion (see illustration) is a perfectly plain oaken arm-chair with four legs connected by cross-bars. The wood is much worm-eaten, and pieces have been cut from various spots at different times, evidently for relics. To the right and left of the seat four strong iron rings, intended for carrying-poles, are set into the legs. At a later date, perhaps in the ninth century, this famous chair was strengthened by the addition of pieces of acacia wood. The latter wood has inlaid in it a rich ornamentation of ivory. For the adornment of the front of the seat eighteen small panels of ivory have been used, on which the labours of Hercules, also fabulous animals, have been engraved; in like manner it was common at this period to ornament the covers of books and reliquaries with ivory panels or carved stones representing mythological scenes. The back is divided by small columns and arches into four fields and finishes at the top in a tympanum which has for ornamentation a large round opening between two smaller ones. The tympanum is surrounded on all sides by strips of ivory engraved in arabesques. At the centre of the horizontal strip a picture of an emperor (not seen in the illustration) is carved in the ivory; it is held to be a portrait of Charles the Bald. The arabesque of acanthus leaves filled with fantastic representations of animals, and the rough execution of the work, would make the period of this emperor (884) a probable date. What still remains of the old cathedra scarcely permits an opinion as to the original form. In any case it was a heavy chair made of plain, straight pieces of wood, so that it cannot be considered a sella curulis of Pudens, as earlier tradition held it to be. If the four rings on the two sides belong to the original chair (Ennodius of Pavia about the sixth century used the term sedes gestatoria as an expression universally understood in reference to this chair), then it was probably an ordinary carrying-chair, such as was commonly used in ancient Rome.
While the two chairs were the visible memorials of the earliest origins of Peter's Apostolic work at Rome, the recollection of his first arrival in the city is stil preserved in the litanioe majores (greater litanies) on 25 April. On this day is also celebrated the feast of St. Mark, whom St. Peter had sent to Alexandria in Egypt. Antioch and Alexandria, the two most important patriarchates of the East, were, in common with Rome, founded by Peter. Gregory the Great refers as follows to this spiritual relationship with the Roman Patriarchate of the West, in a letter to the Patriarch Eulogius (P.L., LXXVII, 899): "Quum multi sint Apostoli, pro ipso autem principatu sola Apostolorum principis sedes in auctoritate convaluit, quæ in tribus locis unius est. Ipse enim sublimavit sedem, in quâ etiam quiescere et præsertim vitam finire dignatus est. Ipse decoravit sedem, in quâ Evangelistam (Marcum) discipulum misit. Ipse firmavit sedem, in quâ septem annis, quamvis discessurus, sedit. Quum ergo unius atque una sit sedes, cui ex auctoritate divinâ tres nunc episcopi præsident, quidquid ego de vobis boni audio, hoc mihi imputo" (Though there are many Apostles, pre-eminence of authority belongs permanently to none other than the Chair of the Prince of the Apostles, which Chair though established in three places remains nevertheless that of one and the same [Apostle]. He lifted it to the highest dignity in the place [Rome] where he deigned to fix his residence and end his life. He honoured it in the city [Alexandria] to which he sent his disciple, the Evangelist Mark. He strengthened it in the city [Antioch] where, though destined to depart, he sat for seven years. Since therefore the Chair in which now by divine authority three bishops preside is the identical chair of the self-same [Peter], I take myself whatever good I hear concerning you).