-On the authoritative magisterium at the beginning of Christianity:
en.wikipedia.org/wiki/Pope_Linus
Linus (died c. AD 76) was, according to several early sources, the second Bishop of Rome, and is listed by the Roman Catholic church as the second pope.
The earliest witness to Linus’s status as bishop was** Irenaeus, who in about the year 180 wrote, "The blessed apostles, then, having founded and built up the Church, committed into the hands of Linus the office of the episcopate.
**
Acts 11:26
And when he had found him, he brought him unto Antioch. And it came to pass, that a whole year they assembled themselves with the church, and taught much people.** And the disciples were called Christians first in Antioch.
**
en.wikipedia.org/wiki/Ignatius_of_Antioch
Ignatius of Antioch (35 AD - 108 AD)was an Apostolic Father, the
third bishop of Antioch[2][3] and a student of John the Apostle. En route to Rome, where he met his martyrdom by being fed to wild beasts, he wrote a series of letters which have been preserved as an example of very early Christian theology. Important topics addressed in these letters include ecclesiology, the sacraments, and the role of bishops.
Ignatius’s letters:
earlychristianwritings.com/text/ignatius-smyrnaeans-roberts.html
CHAPTER VIII.–LET NOTHING BE DONE WITHOUT THE BISHOP.
See that ye all follow the bishop, even as Jesus Christ does the Father, and the presbytery as ye would the apostles; and reverence the deacons, as being the institution of God. Let no man do anything connected with the Church without the bishop.
Let that be deemed a proper Eucharist, which is[administered] either by the bishop, or by one to whom he has entrusted it. Wherever the bishop shall appear, there let the multitude[of the people] also be; even as, wherever Jesus Christ is, there is the Catholic Church. It is not lawful without the bishop either to baptize or to celebrate a love-feast; but whatsoever he shall approve of, that is also pleasing to God, so that everything that is done may be secure and valid.
CHAPTER IX.–HONOUR THE BISHOP.
Moreover, it is in accordance with reason that we should return to soberness[of conduct], and, while yet we have opportunity, exercise repentance towards God. It is well to reverence both God and the bishop.** He who honours the bishop has been honoured by God; he who does anything without the knowledge of the bishop, does[in reality] serve the devil.** Let all things, then, abound to you through grace, for ye are worthy. Ye have refreshed me in all things, and Jesus Christ[shall refresh] you. Ye have loved me when absent as well as when present. May God recompense you, for whose sake, while ye endure all things, ye shall attain unto Him.
earlychristianwritings.com/text/ignatius-smyrnaeans-roberts.html
CHAPTER III.–AVOID SCHISMATICS.
Keep yourselves from those evil plants which Jesus Christ does not tend, because they are not the planting of the Father. Not that I have found any division among you, but exceeding purity. For as many as are of God and of Jesus Christ are also with the bishop. And as many as shall, in the exercise of repentance, return into the unity of the Church, these, too, shall belong to God, that they may live according to Jesus Christ. Do not err, my brethren. **If any man follows him that makes a schism in the Church, he shall not inherit the kingdom of God. **If any one walks according to a strange opinion, he agrees not with the passion [of Christ.].
CHAPTER IV.–HAVE BUT ONE EUCHARIST, ETC.
Take ye heed, then, to have but one Eucharist. For there is one flesh of our Lord Jesus Christ,
and one cup to [show forth] the unity of His blood; one altar; as there is one bishop, along with the presbytery and deacons, my fellow-servants: that so, whatsoever ye do, ye may do it according to [the will of] God.