The historical lists of the popes, from those drawn up in the second century to those of the present day, form in themselves a considerable body of literature. It would be beyond the scope of the article to enter upon a discussion of these catalogues. For an account of the most famous of them all, the article LIBER PONTIFICALIS may be consulted. It appears, however, desirable to indicate very briefly what are our authorities for the names and the durations in office of the popes for the first two centuries of the Church's existence.

St. Irenaeus, writing between 175 and 190, not many years after his Roman sojourn, enumerates the series from Peter to Eleutherius (Against Heresies III.3.3; Eusebius, Church History V.6). His object, as we have already seen, was to establish the orthodoxy of the traditional doctrine, as opposed to heretical novelties, by showing that the bishop was the natural inheritor of the Apostolic teaching. He gives us the names alone, not the length of the various episcopates. This need is supplied by other witnesses.

Most important evidence is furnished by the document entitled the "Liberian Catalogue" – so called from the Pope whose name ends the list. The collection of tracts of which this forms a part was edited (apparently by one Furius Dionysius Philocalus) in 354. The catalogue consists of a list of the Roman bishops from Peter to Liberius, with the length of their respective episcopates, the consular dates, the name of the reigning emperor, and in many cases other details. There is the strongest ground for believing that the earlier part of the catalogue, as far as Pontian (230-35), is the work of Hippolytus of Portus. It is manifest that up to this point the fourth century compiler was making use of a different authority from that which he employs for the subsequent popes: and there is evidence rendering it almost certain that Hippolytus's work "Chronica" contained such a list. The reign of Pontian, moreover, would be the point at which that list would have stopped: for Hippolytus and he were condemned to servitude in the Sardinian mines – a fact which the chronographer makes mention when speaking of Pontian's episcopate. Lightfoot has argued that this list originally contained nothing but the names of the bishops and the duration of their episcopates, the remaining notes being additions by a later hand. The list of popes is identical with that of Irenaeus, save that Anacletus is doubled into Cletus and Anacletus, while Clement appears before, instead of after, these two names. The order of Popes Pius and Anicetus has also been interchanged. There is every reason to regard these differences as due to the errors of copyists.

Another witness is Eusebius. The names and episcopal years of the bishops can be gathered alike from his "History" and his "Chronicle". The notices in the two works; can be shown to be in agreement, notwithstanding certain corruptions in many texts of the "Chronicle". This Eastern list in the hands of Eusebius is seen to have been identical with the Western list of Hippolytus, except that in the East the name of Linus's successor seems to have been given as Anencletus, in the original Western list as Cletus.

The two authorities presuppose the following list: (1) Peter, xxv; (2) Linus, xii; (3) Anencletus [Cletus], xii; (4) Clement, ix; (5) Evarestus, viii; (6) Alexander, x; (7) Sixtus, x; (8) Telesophorus, xi; (9) Hyginus, iv; (10) Pius, xv; (11) Anicetus, xi;, (12) Soter, viii; (13) Eleutherius, xv; (14) Victor, x; (15) Zephyrinus, xviii; (16) Callistus, v; (17) Urban, viii; (18) Pontian, v (Harnack, "Chronologie", I, 152).

We learn from Eusebius (Church History IV.22) that in the middle of the second century Hegesippus, the Hebrew Christian, visited Rome and that he drew up a list of bishops as far as Anicetus, the then pope. Eusebius does not quote his catalogue, but Lightfoot sees ground for holding that we possess it in a passage of Epiphanius (Haer. 27:6), in which the bishops as far as Anicetus are enumerated. This list of Hegesippus, drawn up less than a century after the martyrdom of St. Peter, was he believes, the foundation alike of the Eusebian and Hippolytan catalogues (Clement of Rome I, 325 so.). His view has been accepted by many scholars. Even those who, like Harnack (Chronologie, I, 184 sq.), do not admit that this list is really that of Hegesippus, recognize it as a catalogue of Roman origin and of very early date, furnishing testimony independent alike of the Eusebian and Liberian lists.

The "Liber Pontificalis", long accepted as an authority of the highest value, is now acknowledged to have been originally composed at the beginning of the fifth century, and, as regards the early popes, to be dependent on the "Liberian Catalogue".

In the numbering of the successors of St. Peter, certain differences appear in various lists. The two forms Anacletus and Cletus, as we have seen, very early occasioned the third pope to be reckoned twice. There are some few cases, also, in which it is still doubted whether particular individuals should be accounted genuine popes or intruders, and, according to the view taken by the compiler of the list, they will be included or excluded. In the accompanying list the Stephen immediately following Zacharias (752) is not numbered, since, though duly elected, he died before his consecration. At that period the papal dignity was held to be conferred at consecration, and hence he is excluded from all the early lists. Leo VIII (963) is included, as the resignation of Benedict V, though enforced, may have been genuine. Boniface VII is also ranked as a pope, since, in 984 at least, he would seem to have been accepted as such by the Roman Church. The claim of Benedict X (1058) is likewise recognized. It cannot be affirmed that his title was certainly invalid, and his name, though now sometimes excluded, appears in the older catalogues.

It should be observed that there is no John XX in the catalogue. This is due to the fact that, in the "Liber Pontificalis", two dates are given in connexion with the life of John XIV (983). This introduced confusion into some of the papal catalogues, and a separate pope was assigned to each of these dates. Thus three popes named John were made to appear between Benedict VII and Gregory V. The error led the pope of the thirteenth century who should have been called John XX to style himself John XXI (Duchesne, "Lib. Pont." 2:17).

Some only of the antipopes find mention in the list. No useful purpose would be served by giving the name of every such claimant. Many of them possess no historical importance whatever. From Gregory VII onward not merely the years but the precise days are assigned on which the respective reigns commenced and closed. Ancient authorities furnish these details in the case of most of the foregoing popes also: but, previously to the middle of the eleventh century, the information is of uncertain value. With Gregory VII a new method of reckoning came in. The papal dignity was held to be conferred by the election, and not as previously by the coronation, and the commencement of the reign was computed from the day of election. This point seems therefore a convenient one at which to introduce the more detailed indications.

For the full list of men who have held this office, see LIST OF POPES.