Also 'Sixtus' means literally 'sixth' which seems to apply to Xystus. Irenaeus literally calls Xystus "sixth from the apostles." So you have to wonder if this is an actual 'pope' or another corruption.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).
And finally and most provocatively - Victor and Anicetus. νικητής literally means 'victor.' If Anencletus and Cletus can be understood to be the same, isn't it at all possible that Victor and Anicetus are one and the same?